worker: don't leak watch messages to listeners

[bitpshr]

Under node --watch, each worker reports its module dependencies to the watch supervisor over the worker's message channel. The main thread forwarded those watch:require/watch:import messages to the supervisor but then still emitted them to user worker.on('message') listeners, so applications received undocumented internal messages. It reproduces with node --watch on a script that spawns a Worker (even an empty one).

This consumes the forwarded watch dependency messages instead of surfacing them to user listeners. The main process's own dependency reports go through a separate process.send path in the loader, so watch tracking is unaffected.

The added regression test fails before the change (the watch:require messages reach the user listener) and passes after.

Fixes: #65044

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.28%. Comparing base (4a5eb1c) to head (fbe4f64).
⚠️ Report is 168 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65049      +/-   ##
==========================================
+ Coverage   90.15%   90.28%   +0.13%     
==========================================
  Files         744      759      +15     
  Lines      242517   247637    +5120     
  Branches    45688    46693    +1005     
==========================================
+ Hits       218642   223585    +4943     
- Misses      15358    15509     +151     
- Partials     8517     8543      +26     

Files with missing lines	Coverage Δ
lib/internal/worker.js	96.78% <100.00%> (+0.03%)	⬆️

... and 160 files with indirect coverage changes

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[bitpshr]

Hi @nodejs/workers, wanted to keep this on your radar. Small fix with a regression test, green since August. Happy to rebase if needed.