refactor: flatten nested test helpers and remove any types

[cryptodev-2s]

Explanation

Tests with RPC failover required triple-nested withMockedCommunications blocks, creating excessive indentation and reducing readability. Test helpers also used 20+ instances of any types.

Solution

• Added mockedEndpoints array option to withNetworkClient - eliminates nested blocks
• Replaced any types with proper types (Json, unknown, generics)
• Reduced test indentation from 3 levels to 1 level

Before

await withMockedCommunications({ ... }, async (primaryComms) => {
  await withMockedCommunications({ ... }, async (failoverComms) => {
    await withNetworkClient({ ... }, async ({ ... }) => {
      // test logic
    });
  });
});

After

await withNetworkClient({
  mockedEndpoints: [
    { providerType: networkClientType },
    { providerType: 'custom', customRpcUrl: failoverEndpointUrl },
  ],
}, async ({ comms }) => {
  const [primaryComms, failoverComms] = comms;
  // test logic
});

References

Checklist

• 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
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them