FileContainer: "filename" to "path" and Index

[mathause]

• towards FileContainer: assorted issues #111 points 4. and 5.

Renames the "filename" column of FileContainer to "path" and makes it a pd.Index. The biggest work was actually to fix the tests. It also adds some new tests for the FileContainer.

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 96.28%. Comparing base (5f38744) to head (493dd1d).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
filefinder/_filefinder.py	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #113      +/-   ##
==========================================
+ Coverage   88.85%   96.28%   +7.43%     
==========================================
  Files           5        5              
  Lines         296      296              
==========================================
+ Hits          263      285      +22     
+ Misses         33       11      -22     

Flag	Coverage Δ
unittests	96.28% <90.00%> (+7.43%)	⬆️

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[mathause]

@veni-vidi-vici-dormivi if you want to have a look - otherwise it's also ok for me

[mathause]

Thanks 🤗