Fix async/event lifecycle edge cases

[dmulcahey]

Summary

Fixes async lifecycle edge cases in concurrency limiting, periodic polling cancellation, and async event listener handling.

Failing tests addressed

• tests/test_async_.py::test_gather_with_limited_concurrency_zero_limit_rejected
• tests/test_async_.py::test_periodic_cancellation_propagates
• tests/test_event.py::test_event_base_once_async_multiple_emits_same_tick
• tests/test_event.py::test_event_base_emit_async_callable_object

Verification

• pytest (branch-local targeted run): all listed tests pass.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.51%. Comparing base (9d03d63) to head (1f15a84).
⚠️ Report is 30 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #687      +/-   ##
==========================================
- Coverage   97.51%   97.51%   -0.01%     
==========================================
  Files          62       62              
  Lines       10949    10947       -2     
==========================================
- Hits        10677    10675       -2     
  Misses        272      272              

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[dmulcahey]

for:

Updated the periodic decorator to re-raise CancelledError instead of swallowing it, ensuring correct cancellation propagation for periodic tasks.

Is this one we were preventing propagation of on purpose?

[dmulcahey]

Closing as superseded by the refreshed #829. That PR focuses on the demonstrated event bugs: once-listeners firing more than once and callback-returned awaitables being ignored. The unrelated periodic-cancellation and zero-limit changes from this older PR were not retained because the review did not establish a current need for them.