test_runner: add handleSignals option to run()

[mete0rfish]

Implements the TODO from #43977

---

The built-in test runner already handles SIGINT and SIGTERM, marking any running tests as interrupted before exiting. The run() API, however, did not provide a way to enable the same behavior.

This change adds an opt-in handleSignals option for test runner integrations:

run({
  files: ['test.js'],
  handleSignals: true,
});

Signal handling remains disabled by default, so existing run() users that manage process signals themselves are unaffected. Custom runners can now opt in when they need behavior consistent with the CLI test runner.

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner

[codecov]

Codecov Report

❌ Patch coverage is 82.35294% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.27%. Comparing base (e6a8d06) to head (0bfc0f9).
⚠️ Report is 291 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/test_runner/harness.js	75.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64357      +/-   ##
==========================================
- Coverage   92.01%   90.27%   -1.75%     
==========================================
  Files         379      741     +362     
  Lines      166972   241004   +74032     
  Branches    25554    45422   +19868     
==========================================
+ Hits       153639   217558   +63919     
- Misses      13041    15018    +1977     
- Partials      292     8428    +8136     

Files with missing lines	Coverage Δ
lib/internal/test_runner/runner.js	94.45% <100.00%> (+0.39%)	⬆️
lib/internal/test_runner/harness.js	93.10% <75.00%> (+4.97%)	⬆️

... and 548 files with indirect coverage changes

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