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

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.56%. Comparing base (53cc9df) to head (73da13e).

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)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.