test: mock RPC URL module in Safe sig verifier tests

Without this patch the Safe signature verification code will get RPC
URLs for the specified chain id. This in turn will load the Alchemy API
key, which is not relevant for our tests.

This patch mocks all of this away, so that the API key doesn't need to
be present in the environment while running tests.

Author: pheuberger

test/safe-signatures/SafeSignatureVerifier.test.ts

@@ -1,6 +1,19 @@
-import { describe, it, expect } from "vitest";
+import { describe, it, expect, vi } from "vitest";
 import Verifier from "../../src/lib/safe-signature-verification/UserUpsertSignatureVerifier.js";
 
+// Mock the entire getRpcUrl module
+vi.mock("../../src/utils/getRpcUrl.js", () => ({
+  getRpcUrl: vi.fn().mockImplementation((chainId: number) => {
+    if (chainId === 1) {
+      throw new Error("Unsupported chain ID: 1");
+    }
+    return "mock-rpc-url";
+  }),
+  getEvmClient: vi.fn().mockReturnValue({
+    verifyMessage: vi.fn().mockResolvedValue(true),
+  }),
+}));
+
 // Testing hashing of typed data via UserUpsertSignatureVerifier
 describe("hashTypedMessage", () => {
   it("should hash the typed message correctly", () => {