fix: Event waiter mailbox growth on busy channels

[ftes]

Event waiters retained unrelated protocol events for their subscribed channel. A waiter using timeout: :infinity could accumulate those messages indefinitely.

Discard unrelated events and check the original deadline before receiving again, so queued traffic cannot postpone an expired timeout. Add regression coverage for mailbox draining, independent subscribers, and timeout enforcement, plus module documentation and a changelog entry.

Addresses the review comment on #87.

Validation

• Both new regression tests failed before the fix and pass afterward.
• mix check: formatting, Credo, compilation, Dialyzer, and all 211 tests passed.
• All 211 tests passed over WebSocket using a local Playwright server; Docker was unavailable for the container-based runner.
• mix docs --warnings-as-errors passed.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-15T08:22:38.543576Z	ed29491	PR opened

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