[ChrisJBurns]

Summary

• Adds fmt.Stringer implementation to telemetry.Config that redacts Headers values with [REDACTED] while preserving keys
• Adds fmt.GoStringer implementation (GoString()) to prevent credential leakage via %#v format verb
• Prevents accidental credential leakage (API keys, bearer tokens) if the config struct is logged or printed in error paths
• Includes compile-time interface assertions for both fmt.Stringer and fmt.GoStringer

Parent issue: #3399

Test plan

• TestConfigString_HeaderRedaction — table-driven test covering:
  • Single header redaction (keys visible, values replaced with [REDACTED])
  • Multiple headers redaction
  • Empty headers (no [REDACTED] in output)
  • Nil headers (no panic, no [REDACTED])
  • GoString() delegates to String() in all cases
  • %#v format verb uses GoString() in all cases
• go vet ./pkg/telemetry/... passes
• task lint-fix — 0 issues

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.51%. Comparing base (15eaa3c) to head (e645130).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3782      +/-   ##
==========================================
- Coverage   66.56%   66.51%   -0.05%     
==========================================
  Files         434      434              
  Lines       42309    42321      +12     
==========================================
- Hits        28161    28150      -11     
- Misses      11998    12019      +21     
- Partials     2150     2152       +2     

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