fix(redirect): remove body headers after POST-to-GET

[Ram-blip]

This relates to...

RedirectHandler converts POST requests to GET for 301 and 302 redirects and removes the request body, but it currently keeps body-related Content-* headers on the redirected request.

For example, a redirected bodyless GET can still include Content-Type: application/json and Content-Language: en.

Rationale

Headers describing the original request body should not be forwarded after the redirect changes the method to GET and removes the body.

This change applies the existing content-header cleanup used for 303 redirects when a 301 or 302 redirect converts POST to GET.

Changes

Features

N/A

Bug Fixes

• Remove Content-* headers when a 301 or 302 redirect changes POST to GET.
• Preserve unrelated request headers.
• Add a regression test covering the behavior through Client, Pool, and Agent.

Breaking Changes and Deprecations

None.

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 93.44%. Comparing base (197a83d) to head (e1f242c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5551   +/-   ##
=======================================
  Coverage   93.44%   93.44%           
=======================================
  Files         110      110           
  Lines       37443    37446    +3     
=======================================
+ Hits        34987    34992    +5     
+ Misses       2456     2454    -2     

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[mcollina]

Lgtm