docs(errors): clarify timeout error codes and related options

[theamodhshetty]

Summary

This improves timeout-related error documentation in docs/docs/api/Errors.md.

It adds:

• a dedicated timeout error section that maps codes to when they are thrown
• direct links from each timeout code to the relevant configuration options (connect.timeout, headersTimeout, bodyTimeout)
• a note clarifying that UND_ERR_SOCKET_TIMEOUT is not an Undici error code
• a fetch-oriented example showing how to configure timeouts via setGlobalDispatcher

This is intended to make issues like UND_ERR_*_TIMEOUT easier to understand and act on, especially for users coming from fetch.

Closes #1865.

Testing

• Documentation-only change.
• npm run lint was attempted locally before dependencies were installed, so eslint was not available in this environment.

[metcoder95]

I'd suggest to remove this, as it can lead to ambiguity and misunderstanding; rather let's just list the codes we support so any code outside of the list can be understood as non supported or non originated from undici

[theamodhshetty]

Agreed. I removed that note in 379617c so the section only documents the supported Undici error codes and does not speculate about unsupported ones.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.15%. Comparing base (0bf0a2a) to head (379617c).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4856   +/-   ##
=======================================
  Coverage   93.14%   93.15%           
=======================================
  Files         109      109           
  Lines       34239    34254   +15     
=======================================
+ Hits        31893    31910   +17     
+ Misses       2346     2344    -2     

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