fix: prometheus multproc dir permissions error

[matthewelwell]

This is another implementation of #118 .

Whereas #118 keeps everything well organised in the prometheus package, at the expense of adding complexity to prometheus.__init__, this PR opts for a more simple, but perhaps more crude approach by just implementing all of the logic in the core package.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.65%. Comparing base (4897567) to head (051d617).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #120      +/-   ##
==========================================
+ Coverage   94.63%   94.65%   +0.02%     
==========================================
  Files          77       77              
  Lines        2459     2471      +12     
==========================================
+ Hits         2327     2339      +12     
  Misses        132      132              

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[khvn26]

This looks cleaner and more maintainable than #118, but we need to fix coverage.

[matthewelwell]

This looks cleaner and more maintainable than #118, but we need to fix coverage.

Coverage sorted.