feat(ghcache): diff between manifest and cache

[bassosimone]

This pull request implements generating a diff of the manifest and the cache contents and uses this new functionality to refactor ./data/ghcache.py. In turn, the new code is a refactoring and improvement of the original ./data/ghcache.py code.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.25%. Comparing base (d4926f4) to head (02d9b0d).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #132      +/-   ##
==========================================
+ Coverage   99.18%   99.25%   +0.07%     
==========================================
  Files          38       40       +2     
  Lines        2319     2557     +238     
==========================================
+ Hits         2300     2538     +238     
  Misses         19       19              

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