Add caching of pi-gen artifacts

[usimd]

Adds a new feature to allow caching of pi-gen build container. If a cache hit is found the container is loaded back into the Docker daemon and pi-gen is instructed to continue from the existing container.

[codecov]

Codecov Report

❌ Patch coverage is 99.18699% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 98.86%. Comparing base (4ff4525) to head (af5e183).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/cache.ts	98.64%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #106      +/-   ##
==========================================
+ Coverage   98.45%   98.86%   +0.40%     
==========================================
  Files          13       16       +3     
  Lines         519      618      +99     
  Branches      118      135      +17     
==========================================
+ Hits          511      611     +100     
+ Misses          8        7       -1     

Flag	Coverage Δ
unittests	98.86% <99.18%> (+0.40%)	⬆️

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[JanLahmann]

This pi-gen caching feature would be very helpful and could save a lot of time during development.
Is it possible to test it, already?

[usimd]

Unfortunately not. I did not find enough time lately to continue working on this and the current approach is just a sketchy idea, no clue if that is actually going to improve anything.

If you would like to contribute, feel free to fork from the existing branch.