fix(recovery): mask Cookie and Proxy-Authorization in panic dumps

[sonnemusk]

Summary

secureRequestDump is used when Recovery middleware logs a panic. Previously only Authorization was redacted, so session cookies and proxy credentials could still appear in logs.

This change also masks:

• Cookie
• Proxy-Authorization

Header matching is done by field name (case-insensitive) so the dump stays stable across http.Header canonicalization.

Test plan

• Extended TestSecureRequestDump for Cookie / Proxy-Authorization / multi-header cases
• go test -count=1 -run TestSecureRequestDump .
• go test -count=1 .

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.39%. Comparing base (3dc1cd6) to head (420ba0f).
⚠️ Report is 289 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4744      +/-   ##
==========================================
- Coverage   99.21%   98.39%   -0.82%     
==========================================
  Files          42       48       +6     
  Lines        3182     3181       -1     
==========================================
- Hits         3157     3130      -27     
- Misses         17       41      +24     
- Partials        8       10       +2     

Flag	Coverage Δ
	?
--ldflags="-checklinkname=0" -tags sonic	98.38% <100.00%> (?)
-tags go_json	98.25% <100.00%> (?)
-tags nomsgpack	98.30% <100.00%> (?)
go-1.18	?
go-1.19	?
go-1.20	?
go-1.21	?
go-1.25	98.39% <100.00%> (?)
go-1.26	98.33% <100.00%> (?)
macos-latest	98.33% <100.00%> (-0.89%)	⬇️
ubuntu-latest	98.39% <100.00%> (-0.82%)	⬇️

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