fix: migration script of update MegaETH testnet v2 (#38573)

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## **Description**

This PR fix the migration script 184,
to not replace the network configuration for a user if he already has
megaETH testnet v2 exist
instead we only merge the information


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## **Changelog**

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CHANGELOG entry: Fixed the migration script for adding MegaETH testnet
v2

## **Related issues**

Fixes:

## **Manual testing steps**

1. Install a extension without MegaETH testnet v2
2. Manually add MegaETH testnet v2 config
```
MEGAETH_TESTNET_V2_CONFIG = {
  chainId: '0x18c7', // 6343
  name: 'MegaETH Testnet',
  nativeCurrency: 'MegaETH',
  blockExplorerUrls: ['https://megaeth-testnet-v2.blockscout.com'],
  defaultRpcEndpointIndex: 0,
  defaultBlockExplorerUrlIndex: 0,
  rpcEndpoints: [
    {
      type: RpcEndpointType.Custom,
      url: 'https://timothy.megaeth.com/rpc',
    },
  ],
};
```
3. select the MegaETH testnet v2 as current network
4. update the extension to have the migration run
5. the network should remain the same

## **Screenshots/Recordings**

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before and after of your change. -->

### **Before**
<img width="300" alt="image"
src="https://github.com/user-attachments/assets/b5eba40d-f044-45a9-8c17-6349e56c886a"
/>

<!-- [screenshots/recordings] -->

### **After**

<!-- [screenshots/recordings] -->
<img width="300" alt="image"
src="https://github.com/user-attachments/assets/f8de66ef-37f7-4762-a5f7-af129519b265"
/>

## **Pre-merge author checklist**

- [ ] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask
Extension Coding
Standards](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [ ] I've completed the PR template to the best of my ability
- [ ] I’ve included tests if applicable
- [ ] I’ve documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [ ] I’ve applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Update migration 184 to merge an existing MegaETH Testnet v2 config
instead of overwriting, add it to the enabled map only if missing, and
retain v1-to-mainnet switching; add a test for the merge path.
> 
> - **Migration 184**:
>   - Merge existing `MEGAETH_TESTNET_V2_CONFIG` instead of overwriting:
>     - Update `name` and `nativeCurrency`.
> - Append missing RPC endpoint and block explorer URL; set default
indices accordingly.
>   - Add v2 to `enabledNetworkMap` only if absent.
> - Keep logic to switch selected client from v1 to `mainnet` and remove
v1 config.
> - **Tests**:
>   - Add test to verify merging behavior when v2 already exists.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
9b4283d. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: stanleyyconsensys

app/scripts/migrations/184.test.ts

@@ -220,6 +220,69 @@ describe(`migration #${VERSION}`, () => {
     expect(newStorage).toStrictEqual(expectedStorage);
   });
 
+  it('merges the megaeth testnet v2 network configuration if user already has it', async () => {
+    const oldStorage = {
+      meta: { version: oldVersion },
+      data: {
+        NetworkController: {
+          networkConfigurationsByChainId: {
+            [MEGAETH_TESTNET_V2_CONFIG.chainId]: {
+              ...MEGAETH_TESTNET_V2_CONFIG,
+              name: 'MegaETH Testnet custom',
+              rpcEndpoints: [
+                {
+                  networkClientId: 'some-network-client-id',
+                  type: RpcEndpointType.Custom,
+                  url: 'https://timothy.megaeth.com/rpc',
+                  failoverUrls: [],
+                },
+              ],
+            },
+          },
+        },
+        NetworkEnablementController: {
+          enabledNetworkMap: {
+            [KnownCaipNamespace.Eip155]: {
+              [MEGAETH_TESTNET_V2_CONFIG.chainId]: true,
+            },
+          },
+        },
+      },
+    };
+
+    const expectedStorage = {
+      meta: { version: VERSION },
+      data: {
+        NetworkController: {
+          networkConfigurationsByChainId: {
+            [MEGAETH_TESTNET_V2_CONFIG.chainId]: {
+              ...MEGAETH_TESTNET_V2_CONFIG,
+              rpcEndpoints: [
+                {
+                  networkClientId: 'some-network-client-id',
+                  type: RpcEndpointType.Custom,
+                  url: 'https://timothy.megaeth.com/rpc',
+                  failoverUrls: [],
+                },
+              ],
+            },
+          },
+        },
+        NetworkEnablementController: {
+          enabledNetworkMap: {
+            [KnownCaipNamespace.Eip155]: {
+              [MEGAETH_TESTNET_V2_CONFIG.chainId]: true,
+            },
+          },
+        },
+      },
+    };
+
+    const newStorage = await migrate(oldStorage);
+
+    expect(newStorage).toStrictEqual(expectedStorage);
+  });
+
   // @ts-expect-error 'each' function is not recognized by TypeScript types
   it.each(['megaeth-testnet', 'random-network-client-id'])(
     'switchs to mainnet when the selected network client id is in MegaETH Testnet v1 - %s',

app/scripts/migrations/184.ts

@@ -172,17 +172,63 @@ function transformState(state: Record<string, unknown>) {
     enabledNetworkMap: { [KnownCaipNamespace.Eip155]: eip155NetworkMap },
   } = networkEnablementState;
 
-  const megaethTestnetV1Configuration = networkConfigurationsByChainId[
-    MEGAETH_TESTNET_V1_CHAIN_ID
-  ] as unknown as NetworkConfiguration;
+  // Merge the MegaETH Testnet v2 network configuration if user already has it.
+  if (
+    hasProperty(
+      networkConfigurationsByChainId,
+      MEGAETH_TESTNET_V2_CONFIG.chainId,
+    )
+  ) {
+    const megaethTestnetV2Configuration = networkConfigurationsByChainId[
+      MEGAETH_TESTNET_V2_CONFIG.chainId
+    ] as unknown as NetworkConfiguration;
+    megaethTestnetV2Configuration.name = MEGAETH_TESTNET_V2_CONFIG.name;
+    megaethTestnetV2Configuration.nativeCurrency =
+      MEGAETH_TESTNET_V2_CONFIG.nativeCurrency;
+
+    const isEndpointExist = megaethTestnetV2Configuration.rpcEndpoints.find(
+      (rpcEndpoint) =>
+        rpcEndpoint.url === MEGAETH_TESTNET_V2_CONFIG.rpcEndpoints[0].url,
+    );
+    if (!isEndpointExist) {
+      megaethTestnetV2Configuration.rpcEndpoints.push({
+        failoverUrls: [],
+        networkClientId:
+          MEGAETH_TESTNET_V2_CONFIG.rpcEndpoints[0].networkClientId,
+        type: RpcEndpointType.Custom,
+        url: MEGAETH_TESTNET_V2_CONFIG.rpcEndpoints[0].url,
+      });
+      megaethTestnetV2Configuration.defaultRpcEndpointIndex =
+        megaethTestnetV2Configuration.rpcEndpoints.length - 1;
+    }
 
-  // Add the MegaETH Testnet v2 network configuration.
-  networkConfigurationsByChainId[MEGAETH_TESTNET_V2_CONFIG.chainId] =
-    MEGAETH_TESTNET_V2_CONFIG;
+    const isBlockExplorerUrlExist =
+      megaethTestnetV2Configuration.blockExplorerUrls.find(
+        (url) => url === MEGAETH_TESTNET_V2_CONFIG.blockExplorerUrls[0],
+      );
+    if (!isBlockExplorerUrlExist) {
+      megaethTestnetV2Configuration.blockExplorerUrls.push(
+        MEGAETH_TESTNET_V2_CONFIG.blockExplorerUrls[0],
+      );
+      megaethTestnetV2Configuration.defaultBlockExplorerUrlIndex =
+        megaethTestnetV2Configuration.blockExplorerUrls.length - 1;
+    }
+  } else {
+    // Add the MegaETH Testnet v2 network configuration if user doesn't have it.
+    (networkConfigurationsByChainId as Record<string, NetworkConfiguration>)[
+      MEGAETH_TESTNET_V2_CONFIG.chainId
+    ] = MEGAETH_TESTNET_V2_CONFIG as NetworkConfiguration;
+  }
 
-  // Add the MegaETH Testnet v2 network configuration to the enabled network map.
-  eip155NetworkMap[MEGAETH_TESTNET_V2_CONFIG.chainId] = false;
+  // Add the MegaETH Testnet v2 network configuration to the enabled network map if it doesn't exist.
+  if (!hasProperty(eip155NetworkMap, MEGAETH_TESTNET_V2_CONFIG.chainId)) {
+    (eip155NetworkMap as Record<string, boolean>)[
+      MEGAETH_TESTNET_V2_CONFIG.chainId
+    ] = false;
+  }
 
+  const megaethTestnetV1Configuration =
+    networkConfigurationsByChainId[MEGAETH_TESTNET_V1_CHAIN_ID];
   // If the selected network client id is the old MegaETH Testnet v1,
   // then update it to the mainnet
   if (