Enhance typing for mediafile.fields

[semohr]

This PR adds more comprehensive typing to the mediafile/fields.py module using generics. Fields are now typed as MediaField[T] where T corresponds to the out_type of the field. This allows type checkers and IDEs to more accurately infer field types.

Example:

mf = MediaFile(...)
mf.disc  # type: MediaField[int]

Most fields are still MediaField[unknown], but this PR is a partial step toward fully typed fields. Additional PRs will follow to further improve typing across mediafile.

Now might be a good time to have a look at this to not increase the review burden too much.

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.87500% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.34%. Comparing base (a602f02) to head (5315cb5).

Files with missing lines	Patch %	Lines
mediafile/utils/type_conversion.py	90.00%	1 Missing and 1 partial ⚠️
mediafile/fields.py	98.92%	0 Missing and 1 partial ⚠️
mediafile/utils/image.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #97      +/-   ##
==========================================
+ Coverage   93.26%   93.34%   +0.08%     
==========================================
  Files          16       17       +1     
  Lines         817      842      +25     
  Branches      118      115       -3     
==========================================
+ Hits          762      786      +24     
+ Misses         35       34       -1     
- Partials       20       22       +2     

Files with missing lines	Coverage Δ
mediafile/_types.py	100.00% <100.00%> (ø)
mediafile/constants.py	100.00% <100.00%> (ø)
mediafile/fields.py	94.61% <98.92%> (+1.44%)	⬆️
mediafile/utils/image.py	88.88% <87.50%> (-1.74%)	⬇️
mediafile/utils/type_conversion.py	88.88% <90.00%> (-3.01%)	⬇️

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.