fix(async/unstable): harden pooledMapSettled error handling and abort

[tomas-zijdemans]

Harden pooledMapSettled() error handling, abort responsiveness, and resource cleanup.

Bug Fixes

• Source iterable errors now propagate. Previously silently swallowed; now the iterator rejects with the original error after yielding all in-flight settled results.
• Abort signal interrupts slow/stalled async sources. Each it.next() is raced against the signal, so cancellation is immediate instead of waiting for the source to resume.
• Deterministic error priority. Abort reason wins when signal is already aborted at source failure; source error wins otherwise.

Performance

• executing now uses Set instead of Array. This eliminates O(n) indexOf/splice on every task completion.
• Single abort listener per call instead of creating/tearing down one per raceWithSignal() invocation.

Resource Cleanup

• Fallback generator path now cancels the reader and releases the lock in finally on early consumer break.
• it.return() called on abort so source iterables can run cleanup.
• .catch(() => {}) guards on fire-and-forget promises prevent unhandled-rejection noise.

Docs & Tests

• Updated @throws JSDoc to document both rejection modes.
• Added 9 test cases covering: source error propagation, error-vs-abort priority, abort interrupting slow/stalled sources, and early consumer break (including fallback path).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.43%. Comparing base (a3a6ef6) to head (7f4db0b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7093   +/-   ##
=======================================
  Coverage   94.43%   94.43%           
=======================================
  Files         630      630           
  Lines       50566    50602   +36     
  Branches     8969     8988   +19     
=======================================
+ Hits        47750    47786   +36     
  Misses       2247     2247           
  Partials      569      569           

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