fix: cheaper header validator

[ferhatelmas]

What kind of change does this PR introduce?

Refactoring for perf

What is the current behavior?

Header length validation is allocating a buffer.

What is the new behavior?

Merge header validator plugin and s3 header validation.
Replace regex with a for loop of char code, which is faster for shorter strings.
This approach enables counting at the same time to prevent buffer allocation and do only one pass.

Additional context

Handle empty values in user metadata but block empty key.
Add aws prefix into header length check.

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[coveralls]

Coverage Report for CI Build 28202916763

Coverage decreased (-0.01%) to 78.805%

Details

• Coverage decreased (-0.01%) from the base build.
• Patch coverage: 50 of 50 lines across 4 files are fully covered (100%).
• 18 coverage regressions across 2 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

18 previously-covered lines in 2 files lost coverage.

File	Lines Losing Coverage	Coverage
src/internal/http/agent.ts	17	32.56%
src/http/routes/s3/index.ts	1	82.99%

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Coverage Stats

Relevant Lines:	12182
Covered Lines:	10041
Line Coverage:	82.42%
Relevant Branches:	7025
Covered Branches:	5095
Branch Coverage:	72.53%
Branches in Coverage %:	Yes
Coverage Strength:	421.74 hits per line

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💛 - Coveralls