Fixed fileset-hashing

[tclose]

• Fixes Python fileset hashing (i.e. makes FileSet's hashable via hash(), not to be confused with file-contents hashing), which wasn't being inherited by child classes.
• Ensures all datatypes (including fields) can be hashed

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.10 :tada:

Comparison is base (109c3a1) 85.44% compared to head (924555b) 85.54%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #19 +/- ## ========================================== + Coverage 85.44% 85.54% +0.10% ========================================== Files 32 32 Lines 1862 1868 +6 Branches 459 455 -4 ========================================== + Hits 1591 1598 +7 + Misses 197 196 -1 Partials 74 74 ``` | [Impacted Files](https://app.codecov.io/gh/ArcanaFramework/fileformats/pull/19?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ArcanaFramework) | Coverage Δ | | |---|---|---| | [fileformats/generic/\_\_init\_\_.py](https://app.codecov.io/gh/ArcanaFramework/fileformats/pull/19?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ArcanaFramework#diff-ZmlsZWZvcm1hdHMvZ2VuZXJpYy9fX2luaXRfXy5weQ==) | `73.24% <ø> (-0.51%)` | :arrow_down: | | [fileformats/core/fileset.py](https://app.codecov.io/gh/ArcanaFramework/fileformats/pull/19?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ArcanaFramework#diff-ZmlsZWZvcm1hdHMvY29yZS9maWxlc2V0LnB5) | `88.12% <100.00%> (+0.21%)` | :arrow_up: | | [fileformats/field/\_\_init\_\_.py](https://app.codecov.io/gh/ArcanaFramework/fileformats/pull/19?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ArcanaFramework#diff-ZmlsZWZvcm1hdHMvZmllbGQvX19pbml0X18ucHk=) | `84.78% <100.00%> (+1.06%)` | :arrow_up: |

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