fix(proxy agent): respect connectTimeout

[rozzilla]

This relates to...

Fixes #4983.

Rationale

ProxyAgent inherits connectTimeout, but it was not forwarding that value to its internal connectors. This meant proxy connections could still use the default 10-second timeout instead of the configured one.

Changes

• forward connectTimeout to the proxy connector
• forward connectTimeout to the request connectors
• add a regression test for the timeout behavior

Features

n/a

Bug Fixes

n/a

Breaking Changes and Deprecations

n/a

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.92%. Comparing base (0143e1b) to head (b04759c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5011      +/-   ##
==========================================
- Coverage   92.93%   92.92%   -0.01%     
==========================================
  Files         110      110              
  Lines       35739    35739              
==========================================
- Hits        33214    33212       -2     
- Misses       2525     2527       +2     

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