fix: support new handler API in custom dispatchers

[mcollina]

Summary

• wrap handler callbacks only for custom dispatchers so new handler API works without affecting core dispatchers
• add regression coverage for Undici request() from Dispatcher base class only uses undocumented handler API, not new handler API #4780
• remove XHR from WPT run list (unsupported) and refresh expectations after rerun
• ignore local tooling folders

Testing

• npm run test:wpt
• timeout 180 npx borp -p test/client-request.js

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.29%. Comparing base (4b36fef) to head (ec537c7).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/api/api-connect.js	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4785      +/-   ##
==========================================
+ Coverage   93.25%   93.29%   +0.03%     
==========================================
  Files         109      109              
  Lines       34001    34078      +77     
==========================================
+ Hits        31708    31793      +85     
+ Misses       2293     2285       -8     

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