fix(handler): preserve latin1 header encoding in WrapHandler

[theamodhshetty]

Summary

Fixes WrapHandler header/trailer conversion to preserve latin1/isomorphic byte semantics when bridging new handler API -> old handler API.

Today WrapHandler uses Buffer.from(value) (utf-8 default), which can corrupt non-ASCII header bytes when the old API later reads as latin1.

What changed

• Use latin1 encoding when converting wrapped header keys/values to raw buffers in:
  • onRequestUpgrade
  • onResponseStart
  • onResponseEnd
• Added a helper to centralize raw header value conversion.
• Added regression coverage in test/issue-3934.js:
  • WrapHandler preserves latin1 header bytes

Validation

• node --test test/issue-3934.js
• npm run lint

Fixes #4797.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.14%. Comparing base (f734c87) to head (c358b51).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4859   +/-   ##
=======================================
  Coverage   93.13%   93.14%           
=======================================
  Files         109      109           
  Lines       34243    34249    +6     
=======================================
+ Hits        31893    31902    +9     
+ Misses       2350     2347    -3     

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[mcollina]

lgtm