lib: add signalMonitor event for process

[theanarkh]

fixed : #62909

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.64%. Comparing base (c202696) to head (afe1a20).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #62975      +/-   ##
==========================================
- Coverage   89.66%   89.64%   -0.03%     
==========================================
  Files         706      706              
  Lines      219416   219414       -2     
  Branches    42073    42076       +3     
==========================================
- Hits       196738   196687      -51     
- Misses      14576    14647      +71     
+ Partials     8102     8080      -22     

Files with missing lines	Coverage Δ
lib/events.js	99.60% <100.00%> (+<0.01%)	⬆️

... and 50 files with indirect coverage changes

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[yminod]

I tested this change on both Windows and macOS.

With only process.on('signalMonitor', ...) registered, pressing Ctrl+C exits immediately and the signalMonitor listener does not run. By contrast, process.emit('SIGINT') does trigger signalMonitor.

As I understand it, signalMonitor seems to observe synthetic signal emission such as process.emit(), but not the Ctrl+C / OS-delivered signal path by itself.

Because of that, I don't think this resolves #62909 yet. The issue there is about passively observing real signal delivery without installing an active signal handler, so I think the test should cover an actual signal-delivery path, not only process.emit().