🧹 chore: Optimize cache middleware performance

[gaby]

Summary

• avoid holding the cache mutex during storage I/O and reuse fasthttp date handling when serving cached responses
• refactor Cache-Control parsing to reuse parsed directives, using utils.EqualFold for directive comparisons, and clamp duration conversions
• store cached response headers as a slice-backed structure and regenerate msgp code to match

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[gemini-code-assist]

Summary of Changes

Hello @gaby, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on enhancing the performance and efficiency of the cache middleware. It achieves this by optimizing mutex handling to reduce contention during storage operations, refining the parsing of Cache-Control headers for better reuse and accuracy, and restructuring how response headers are stored to improve serialization and retrieval. These changes collectively aim to make the caching mechanism faster and more robust, particularly under high load.

Highlights

• Concurrency Optimization: The cache mutex is no longer held during potentially blocking storage I/O operations, significantly improving concurrency and reducing contention within the cache middleware.
• Efficient Cache-Control Parsing: Cache-Control header parsing has been refactored for greater efficiency, reusing parsed directives, utilizing utils.EqualFold for case-insensitive comparisons, and clamping duration conversions to prevent overflows.
• Optimized Header Storage and Date Handling: Cached response headers are now stored as a slice-backed structure ([]cachedHeader) instead of a map, and fasthttp's highly optimized date handling is leveraged for improved performance when serving cached responses.
• Serialization Code Regeneration: The msgp code for serialization and deserialization has been regenerated to accurately reflect the new slice-backed header storage structure, ensuring data integrity and compatibility.

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[codecov]

Codecov Report

❌ Patch coverage is 86.51685% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.92%. Comparing base (d8b3408) to head (4b8608c).
⚠️ Report is 5 commits behind head on update-cache-handling-for-authentication.

Files with missing lines	Patch %	Lines
middleware/cache/cache.go	86.51%	16 Missing and 8 partials ⚠️

Additional details and impacted files

@@                             Coverage Diff                              @@
##           update-cache-handling-for-authentication    #3979      +/-   ##
============================================================================
- Coverage                                     90.99%   90.92%   -0.08%     
============================================================================
  Files                                           119      119              
  Lines                                         10672    10749      +77     
============================================================================
+ Hits                                           9711     9773      +62     
- Misses                                          610      618       +8     
- Partials                                        351      358       +7     

Flag	Coverage Δ
unittests	90.92% <86.51%> (-0.08%)	⬇️

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[gemini-code-assist]

Code Review

This pull request introduces significant performance optimizations to the cache middleware. The changes focus on reducing lock contention by releasing the mutex during I/O operations, which is a great improvement. The refactoring of Cache-Control header parsing to a zero-allocation, single-pass implementation is excellent for performance. Additionally, switching to fasthttp's date handling functions and changing the internal storage of headers from a map to a slice are smart optimizations. The code is cleaner and more efficient. I've found a few minor areas for improvement regarding some redundant lock operations in error handling paths, but overall this is a high-quality contribution.