Fix concurrent intercom reply waiters

[danrom85]

Summary

Fixes a crash/race condition when multiple reply-waiting intercom calls run concurrently.

Previously, pi-intercom used a single module-scoped replyWaiter. If two ask / supervisor-style calls were active at the same time, the second waiter could hit Already waiting for a reply. In Node versions where unhandled rejections are thrown, this can
terminate the Pi process.

This PR changes reply waiting to support independent concurrent waiters keyed by replyTo / question ID.

Changes

• Replace singleton replyWaiter with a Map<string, ReplyWaiter>
• Resolve replies by replyTo, allowing concurrent asks to coexist
• Reject all outstanding waiters on disconnect/shutdown
• Clean up only the current waiter on delivery/cancel/error
• Add .catch(() => undefined) for ask-path reply promises to avoid unhandled rejection crashes
• Add regression coverage for concurrent supervisor asks resolving independently, including out-of-order replies

Validation

• Ran npm install
• Ran npm test
• Result: 37 tests passed