refactor: allow better debugging headers are frozen

[pi0]

When an empty response or JSON response is returned, H3 returns a response with with frozen headers to prevent sharing state across requests.

However currently it might but hard to investigate source of issue (when stack-traces are not helping)

This PR adds operation (set|append|delete) + arguments info to error to allow debugging better. (it costs ~20 bytes of bundle)

Summary by CodeRabbit

• Refactor
  • Enhanced error messaging when attempting to modify frozen headers, providing clearer feedback to developers.

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[coderabbitai]

📝 Walkthrough

Walkthrough

This PR refactors the header immutability mechanism in response handling by replacing a dedicated frozenHeaders function with a generic frozen(name) factory pattern, improving error messaging for modification attempts on frozen headers.

Changes

Cohort / File(s)	Change Summary
Header Immutability Refactoring src/response.ts	Replaces dedicated frozenHeaders function with generic frozen(name) factory. The FrozenHeaders class now uses these frozen wrappers for set, append, and delete operations with enhanced error reporting. No changes to header read/creation behavior.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐰 A frozen header's a stubborn friend,
Now wrapped in factory cheer!
Set, append, delete—they'll always defend,
With messages crystal clear! 🔒✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title accurately describes the main refactoring: improving error messages for frozen headers to enable better debugging by adding operation and argument details.

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✨ Finishing touches

• 📝 Generate docstrings

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[pkg-pr-new]

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npm i https://pkg.pr.new/h3js/h3@1287

commit: 9c8e62d