Replaced DocumentTypes type hint with DocumentTypesBase

[keighrim]

fixes#351

[Copilot]

Pull request overview

This pull request fixes type hint issues in the mmif.Mmif class methods that were causing both pytype errors and runtime crashes when using DocumentTypes in type annotations.

Changes:

• Updated type hints to use DocumentTypesBase instead of DocumentTypes or Any
• Added DocumentTypesBase to imports in mmif/serialize/mmif.py

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.56%. Comparing base (53cc9df) to head (73da13e).
⚠️ Report is 9 commits behind head on develop.

Additional details and impacted files

@@ Coverage Diff @@## develop #353 +/- ##
========================================
Coverage 65.56% 65.56% ========================================
Files 22 22 Lines 2843 2843 ========================================
Hits 1864 1864 Misses 979 979 

Flag	Coverage Δ
unittests	65.56% <100.00%> (ø)

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