feat: External stylesheet caching

[Stranger6667]

Resolves #314

• Configure cache from Python, JS, Ruby, C & CLI
• Consider enabling cache by default - it seems to be useful in general.

[codspeed-hq]

CodSpeed Performance Report

Merging #350 will not alter performance

_{Comparing dd/cache-stylesheets (b9d28c9) with master (ee538f2)}

Summary

✅ 6 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.32%. Comparing base (ee538f2) to head (b9d28c9).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #350      +/-   ##
==========================================
+ Coverage   85.04%   86.32%   +1.28%     
==========================================
  Files          18       18              
  Lines        1759     1814      +55     
==========================================
+ Hits         1496     1566      +70     
+ Misses        263      248      -15     

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