chore: Notification services controller lint cleanup (#7481)

## Explanation

* **What is the current state of things and why does it need to
change?**
The `packages/notification-services-controller` contained ESLint
suppressions for `@typescript-eslint/explicit-function-return-type` and
`@typescript-eslint/prefer-nullish-coalescing`. These suppressions
indicated areas where type safety and modern JavaScript practices were
not fully enforced, leading to potential maintainability issues and
reduced code clarity.

*   **What is the solution your changes offer and how does it work?**
    This PR addresses these suppressions by:
1. Adding explicit return types to functions in
`NotificationServicesPushController.test.ts`,
`NotificationServicesPushController.ts`, and
`__fixtures__/mockServices.ts` to satisfy the
`@typescript-eslint/explicit-function-return-type` rule.
2. Replacing a logical OR (`||`) with the nullish coalescing operator
(`??`) in `NotificationServicesPushController.test.ts` to fix the
`@typescript-eslint/prefer-nullish-coalescing` rule.
3. Removing the corresponding entries for these files and rules from
`eslint-suppressions.json`.

* **Are there any changes whose purpose might not obvious to those
unfamiliar with the domain?**
No, the changes are straightforward type annotations and a minor logical
operator update.

## References

*   Fixes ASSETS-2100

## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
- [ ] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [x] I've communicated my changes to consumers by [updating changelogs
for packages I've
changed](https://github.com/MetaMask/core/tree/main/docs/contributing.md#updating-changelogs)
- [ ] I've introduced [breaking
changes](https://github.com/MetaMask/core/tree/main/docs/breaking-changes.md)
in this PR and have prepared draft pull requests for clients and
consumer packages to resolve them

---
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<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Adds explicit return types across NotificationServicesPushController
code/tests, adopts nullish coalescing in tests, and removes related
ESLint suppressions.
> 
> - **Notification Services Push Controller**:
> - Add explicit return types to `#getAndAssertBearerToken`,
`#updatePushState`, `subscribeToPushNotifications`,
`enablePushNotifications`, `disablePushNotifications`, and
`updateTriggerPushNotifications` in
`NotificationServicesPushController.ts`.
> - **Tests**:
> - Add explicit return types to helpers (`mockErrorLog`,
`arrangeServicesMocks`, `arrangeMockMessenger`,
`mockAuthBearerTokenCall`) and improve Jest typings in
`NotificationServicesPushController.test.ts`.
>   - Use nullish coalescing (`??`) for config defaults.
> - **Mocks**:
> - Add return type to `mockEndpointUpdatePushNotificationLinks` in
`__fixtures__/mockServices.ts`.
> - **ESLint**:
> - Remove suppressions for
`@typescript-eslint/explicit-function-return-type` and
`@typescript-eslint/prefer-nullish-coalescing` entries related to these
files in `eslint-suppressions.json`.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
f5e64a1. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Cursor Agent <[email protected]>

Author: Prithpal-Sooriya

eslint-suppressions.json

@@ -1593,24 +1593,6 @@
       "count": 70
     }
   },
-  "packages/notification-services-controller/src/NotificationServicesPushController/NotificationServicesPushController.test.ts": {
-    "@typescript-eslint/explicit-function-return-type": {
-      "count": 4
-    },
-    "@typescript-eslint/prefer-nullish-coalescing": {
-      "count": 1
-    }
-  },
-  "packages/notification-services-controller/src/NotificationServicesPushController/NotificationServicesPushController.ts": {
-    "@typescript-eslint/explicit-function-return-type": {
-      "count": 6
-    }
-  },
-  "packages/notification-services-controller/src/NotificationServicesPushController/__fixtures__/mockServices.ts": {
-    "@typescript-eslint/explicit-function-return-type": {
-      "count": 1
-    }
-  },
   "packages/notification-services-controller/src/NotificationServicesPushController/services/services.ts": {
     "@typescript-eslint/naming-convention": {
       "count": 1

packages/notification-services-controller/src/NotificationServicesPushController/NotificationServicesPushController.test.ts

@@ -16,11 +16,16 @@ const MOCK_FCM_TOKEN = 'mockFcmToken';
 const MOCK_ADDRESSES = ['0x123', '0x456', '0x789'];
 
 // Testing util to clean up verbose logs when testing errors
-const mockErrorLog = () =>
+const mockErrorLog = (): jest.SpyInstance =>
   jest.spyOn(log, 'error').mockImplementation(jest.fn());
 
 describe('NotificationServicesPushController', () => {
-  const arrangeServicesMocks = (token?: string) => {
+  const arrangeServicesMocks = (
+    token?: string,
+  ): {
+    activatePushNotificationsMock: jest.SpyInstance;
+    deactivatePushNotificationsMock: jest.SpyInstance;
+  } => {
     const activatePushNotificationsMock = jest
       .spyOn(services, 'activatePushNotifications')
       .mockResolvedValue(token ?? MOCK_FCM_TOKEN);
@@ -359,8 +364,12 @@ function arrangeMockMessenger(
       state?: Partial<NotificationServicesPushController['state']>;
     }
   >,
-) {
-  const { state: stateOverride, ...configOverride } = controllerConfig || {};
+): {
+  controller: NotificationServicesPushController;
+  initialState: NotificationServicesPushController['state'];
+  messenger: NotificationServicesPushControllerMessenger;
+} {
+  const { state: stateOverride, ...configOverride } = controllerConfig ?? {};
 
   const config: ControllerConfig = {
     isPushFeatureEnabled: true,
@@ -403,7 +412,14 @@ function arrangeMockMessenger(
  */
 function mockAuthBearerTokenCall(
   messenger: NotificationServicesPushControllerMessenger,
-) {
+): jest.Mock<
+  ReturnType<
+    AuthenticationController.AuthenticationControllerGetBearerToken['handler']
+  >,
+  Parameters<
+    AuthenticationController.AuthenticationControllerGetBearerToken['handler']
+  >
+> {
   type Fn =
     AuthenticationController.AuthenticationControllerGetBearerToken['handler'];
   const mockAuthGetBearerToken = jest

packages/notification-services-controller/src/NotificationServicesPushController/NotificationServicesPushController.ts

@@ -225,7 +225,7 @@ export default class NotificationServicesPushController extends BaseController<
     });
   }
 
-  async #getAndAssertBearerToken() {
+  async #getAndAssertBearerToken(): Promise<string> {
     const bearerToken = await this.messenger.call(
       'AuthenticationController:getBearerToken',
     );
@@ -239,7 +239,7 @@ export default class NotificationServicesPushController extends BaseController<
     return bearerToken;
   }
 
-  #updatePushState(command: StateCommand) {
+  #updatePushState(command: StateCommand): void {
     if (command.type === 'enable') {
       this.update((state) => {
         state.isPushEnabled = true;
@@ -266,7 +266,7 @@ export default class NotificationServicesPushController extends BaseController<
     }
   }
 
-  public async subscribeToPushNotifications() {
+  public async subscribeToPushNotifications(): Promise<void> {
     if (!this.#config.isPushFeatureEnabled) {
       return;
     }
@@ -296,7 +296,7 @@ export default class NotificationServicesPushController extends BaseController<
    *
    * @param addresses - An array of addresses to enable push notifications for.
    */
-  public async enablePushNotifications(addresses: string[]) {
+  public async enablePushNotifications(addresses: string[]): Promise<void> {
     if (!this.#config.isPushFeatureEnabled) {
       return;
     }
@@ -351,7 +351,7 @@ export default class NotificationServicesPushController extends BaseController<
    * Disables push notifications for the application.
    * This removes the registration token on this device, and ensures we unsubscribe from any listeners
    */
-  public async disablePushNotifications() {
+  public async disablePushNotifications(): Promise<void> {
     if (!this.#config.isPushFeatureEnabled) {
       return;
     }
@@ -394,7 +394,9 @@ export default class NotificationServicesPushController extends BaseController<
    * @param addresses - An array of addresses that should trigger push notifications.
    * @deprecated - this is not used anymore and will most likely be removed
    */
-  public async updateTriggerPushNotifications(addresses: string[]) {
+  public async updateTriggerPushNotifications(
+    addresses: string[],
+  ): Promise<void> {
     if (!this.#config.isPushFeatureEnabled) {
       return;
     }

packages/notification-services-controller/src/NotificationServicesPushController/__fixtures__/mockServices.ts

@@ -9,7 +9,7 @@ type MockReply = {
 
 export const mockEndpointUpdatePushNotificationLinks = (
   mockReply?: MockReply,
-) => {
+): nock.Scope => {
   const mockResponse = getMockUpdatePushNotificationLinksResponse();
   const reply = mockReply ?? {
     status: 204,