test: deflake connect-timeout watchdog

[mcollina]

Summary

• deflake the connect-timeout tests by using a shared helper for Client and Pool
• replace the aggressive 2s watchdog with a longer guard that matches FastTimer behavior and the extra Windows setImmediate hop
• use test-scoped cleanup that tolerates an already-closed dispatcher

Testing

• npx borp -p "test/connect-timeout.js"
• npx eslint test/connect-timeout.js

Closes #5187

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.27%. Comparing base (9c12e26) to head (be6f49e).
⚠️ Report is 22 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5197      +/-   ##
==========================================
- Coverage   93.27%   93.27%   -0.01%     
==========================================
  Files         110      110              
  Lines       36241    36313      +72     
==========================================
+ Hits        33805    33870      +65     
- Misses       2436     2443       +7     

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[metcoder95]

merge conflicts