test(integration): stabilize watch helper using run-completion sync

[mostafaNazari702]

PR Checklist

• Addresses an existing open issue: fixes 🛠️ Repo: CI run failures (test failures) #5361
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

This stabilizes test/integration/options/watch.spec.js by removing the brittle startup timing assumption in runMochaWatchAsync.

Before this change, helper timing was based on fixed sleeps (sleepMs) before and after the file change callback. That could miss real watch lifecycle timing on slower/contended CI environments, especially for watch paths outside the current working directory.

What changed:

• runMochaWatchAsync now synchronizes using real watch-run completion markers from subprocess output instead of relying on fixed startup waits.
• After applying the change callback, it waits for watch output to settle (no additional completed runs within the configured interval) before sending SIGINT.
• This keeps behavior for tests expecting no rerun while allowing tests that trigger multiple reruns to complete consistently.

Why this approach:

• It targets the race directly rather than increasing arbitrary delays for a single test.
• It aligns with ongoing direction discussed in 🛠️ Repo: improve speed and reliability of watch mode tests #5714 and fix: begin running tests immediately instead of waiting for watcher, reload required files in watch mode #5409 toward event-driven watch test synchronization.

Validation run:

• npm run test-node:integration:watch → 30 passing
• Repeated CI-like loops for the target test (--parallel --timeout 10000 --slow 3750, grep: outside the current working directory) passed consistently, including under CPU load.

[mostafaNazari702]

Wrong branch.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.71%. Comparing base (e15bbda) to head (f755981).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5879   +/-   ##
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  Coverage   89.71%   89.71%           
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  Files          64       64           
  Lines        4695     4695           
  Branches      978      978           
=======================================
  Hits         4212     4212           
  Misses        483      483           

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[mostafaNazari702]

I was actually right, thought that i pushed code to the previous active PR that i have. Sorry.
I would also like to mention that the PR body was rewritten from my notes, which normally sound like gibberish. using AI.