Fix EventHub listener disposal

[vrtmrz]

Fix EventHub subscription lifecycle handling so caller-provided abort signals and returned disposers affect only their own registration.

Summary

• Honour caller-supplied abort signals in on and onEvent.
• Make returned disposers registration-scoped and idempotent.
• Prevent stale disposers from removing later subscriptions using the same callback.
• Accept AddEventListenerOptions in once and onceEvent.
• Preserve off(event, callback) as a bulk-removal compatibility API.
• Update generated output, API documentation, and release notes.

Verification

• Confirmed seven focused regression cases failed against the previous implementation.
• EventHub tests: 30 passed.
• Octagonal Wheels browser tests: 983 passed.
• Octagonal Wheels Node tests: 4 passed.
• ESLint and TypeScript checks passed.
• Package build, dry-run pack, and built-artefact runtime probe passed.