fix: release waitFor listeners on cancellation

[cevr]

Cancelling actor.waitFor left its state listener registered. Later transitions still called the cancelled wait's predicate. A predicate defect during the subscription recheck leaked the listener too.

Own listener registration with Effect.acquireUseRelease. Keep the current-state fast path and post-subscription recheck. Release on success, defect, and cancellation. Public types and actor stop behavior stay unchanged; awaitFinal and sendAndWait inherit the cleanup.

waitFor
- add listener -> recheck/await -> remove on success
+ acquire listener -> recheck/await -> release on every exit

Validation: both real-actor regressions fail before the fix. Full gate passes: 385 tests, 853 assertions, typecheck, lint, format, build, and all example gates. One independent Counsel review found no blocker. Includes a patch changeset.