feat(cache): compress big sqlite cache entries with zstd

[mcollina]

Store SQLite cache response bodies that are larger than the new compressThreshold option (default 1 MiB) compressed with zstdCompressSync, decompressing them when read back so cached responses still return the exact original body. This lets large cached responses occupy significantly less database space.

The change:

• Adds a compressThreshold option to SqliteCacheStore.
• Adds a compressed column to the cache table (bumping cacheInterceptorV3 to cacheInterceptorV4) so stored bodies know whether to decompress.
• Falls back to storing bodies uncompressed when zstd is unavailable (Node < 22.19), while still requiring node:sqlite.
• Documents the new option in the Cache Store API docs and the SqliteCacheStoreOpts types.
• Adds a test verifying big bodies are stored compressed and round-trip correctly, and that small bodies remain uncompressed.

[ronag]

1 MB is quite big? text and json is quite compressible also for smaller size?

[ronag]

can be good to make this a string and use "zstd", would make it more forward compatible

[mcollina]

Done - the compressed column now stores the algorithm as a string ("zstd") instead of an integer, and get() only decompresses rows whose algorithm is zstd, so future algorithms can be added without breaking existing data.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 93.97590% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.47%. Comparing base (fc3450d) to head (3b07894).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/cache/sqlite-cache-store.js	93.97%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #5744    +/-   ##
========================================
  Coverage   93.47%   93.47%            
========================================
  Files         110      110            
  Lines       38908    39017   +109     
========================================
+ Hits        36368    36473   +105     
- Misses       2540     2544     +4     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[ronag]

I would recommend checking the response mime type to find easily compressible responses, e.g. json, xml, plain text etc... and ignore the compressThreshold for those

[mcollina]

Done - responses with an easily compressible Content-Type (text/*, application/json, application/xml, application/javascript, ...) are now compressed regardless of the compressThreshold. I also guard against pathological inflation: compression only applies when the zstd output is actually smaller than the original body.