Add more support for typing, fix some typing-related edge case bugs

[RalfG]

• Adds full support for typing with MyPy
• Removed support for Python 3.9
• CI: Replaced file hash-based tests for idxml with proper unit tests.
• CI: Add format checks.

[codecov]

Codecov Report

❌ Patch coverage is 79.95246% with 253 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.23%. Comparing base (95e8218) to head (7487324).

Files with missing lines	Patch %	Lines
psm_utils/io/mzid.py	39.02%	50 Missing ⚠️
psm_utils/io/ionbot.py	14.28%	30 Missing ⚠️
psm_utils/io/idxml.py	82.09%	29 Missing ⚠️
psm_utils/io/percolator.py	44.68%	26 Missing ⚠️
psm_utils/io/peptide_record.py	66.66%	22 Missing ⚠️
psm_utils/psm_list.py	46.87%	17 Missing ⚠️
psm_utils/io/tsv.py	48.27%	15 Missing ⚠️
psm_utils/peptidoform.py	75.80%	15 Missing ⚠️
psm_utils/io/__init__.py	62.50%	9 Missing ⚠️
psm_utils/io/pepxml.py	55.00%	9 Missing ⚠️
... and 13 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #125      +/-   ##
==========================================
+ Coverage   69.12%   70.23%   +1.10%     
==========================================
  Files          30       30              
  Lines        2802     3047     +245     
==========================================
+ Hits         1937     2140     +203     
- Misses        865      907      +42     

Flag	Coverage Δ
unittests	70.23% <79.95%> (+1.10%)	⬆️

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