Allow more time for local synchronizer responses

[dajiaohuang]

Summary

Fixes #298.

Restore the LocalSynchronizer request timeout from 10 ms to its earlier 50 ms value. Requests and responses are delivered asynchronously by timers; a 10 ms deadline can expire before an otherwise valid response arrives.

Add a fake-timer regression that delays each zero-delay delivery by 15 ms, and wait for convergence before the prepopulated bidirectional tests inspect their existing expected content and snapshots. No snapshots, dependencies, or public API are changed.

Tradeoff: a missing peer can take an additional 40 ms to time out. This provides headroom for the reproduced timer scheduling behavior, not a guarantee against arbitrary event-loop stalls.

How did you test this change?

• Native compileForTest build passes.
• New delayed-delivery test fails with the original timeout and passes with 50 ms.
• Local synchronizer selection: 62 tests pass.
• Middleware test file: all 336 tests pass, including both sync-back tests that failed with the original deadline on this machine.
• Complete synchronizers file: 234 pass, 11 fail, all in the Custom Synchronizer mock, which uses its own unchanged 5 ms deadline. Removing the new convergence wait reproduces all eleven failures under the original wait logic. No snapshots were updated.
• Source, test, and site TypeScript checks pass. The gulp ts wrapper then hits spawn npx ENOENT on Windows; running its two installed Svelte-check entrypoints directly gives zero errors/warnings in both workspaces.
• Prettier, ESLint for the changed files, and git diff --check pass.

Environment: Windows, Node.js v24.14.1. Full repository test coverage is not claimed.