Splits up generic sub-package into separate modules

[tclose]

• splits up fileformats.generic.init.py into separate sub-modules
• implements relevant methods of pathlib.Path in FsObject

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 80.41958% with 56 lines in your changes are missing coverage. Please review.

Project coverage is 92.66%. Comparing base (feeadef) to head (1cab32c).

Files	Patch %	Lines
fileformats/generic/fsobject.py	71.01%	19 Missing and 1 partial :warning:
fileformats/generic/directory.py	84.41%	10 Missing and 2 partials :warning:
fileformats/generic/file.py	81.13%	7 Missing and 3 partials :warning:
fileformats/generic/set.py	67.74%	5 Missing and 5 partials :warning:
fileformats/generic/generate_sample_data.py	92.00%	2 Missing and 2 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #64 +/- ## ========================================== - Coverage 93.06% 92.66% -0.40% ========================================== Files 40 45 +5 Lines 4816 4909 +93 Branches 537 547 +10 ========================================== + Hits 4482 4549 +67 - Misses 244 270 +26 Partials 90 90 ```

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