fix: use latin1 encoding for headers in WrapHandler

[mcollina]

Summary

• Fix WrapHandler to use Latin1 encoding when converting header strings to Buffers
• Previously used Buffer.from(val) which defaults to UTF-8, causing header values with non-ASCII bytes to be incorrectly encoded
• Affects onRequestUpgrade, onResponseStart, and onResponseEnd methods

Fixes #4797

Test plan

• Verified both repro cases from the issue now work correctly
• All existing unit tests pass (1221 tests)
• Lint passes

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.24%. Comparing base (352c691) to head (3d21fa5).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4798      +/-   ##
==========================================
- Coverage   93.25%   93.24%   -0.02%     
==========================================
  Files         109      109              
  Lines       34024    34100      +76     
==========================================
+ Hits        31729    31796      +67     
- Misses       2295     2304       +9     

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