fix(async): abortable should prevent uncaught error when promise is rejected

[Milly]

In abortable:

• If the signal is aborted with delay and the promise is rejected, an uncaught error does not occur. This is OK.
• If the signal is already aborted and the promise is rejected, an uncaught error occurs.

Uncaught errors should not occur in either case.

Also, I changed the tests to use delay instead of clearTimeout to detect leaks.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.34%. Comparing base (c40f593) to head (8b1850a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6312   +/-   ##
=======================================
  Coverage   96.33%   96.34%           
=======================================
  Files         547      547           
  Lines       41667    41667           
  Branches     6314     6314           
=======================================
+ Hits        40140    40144    +4     
+ Misses       1484     1481    -3     
+ Partials       43       42    -1     

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[kt3k]

The fix looks good to me.

Also, I changed the tests to use delay instead of clearTimeout to detect leaks.

This change makes the test cases flaky like this one https://github.com/denoland/std/actions/runs/12528301271/job/34942765393

Can you revert these changes? (Timers are generally very unreliable in testing)