TokSequence summable, concatenate_track_sequences arg for MMM

[Natooz]

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📚 Documentation preview 📚: https://miditok--173.org.readthedocs.build/en/173/

[codecov]

Codecov Report

Attention: Patch coverage is 82.92683% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 90.32%. Comparing base (5b3c3f6) to head (1cf319c).
Report is 1 commits behind head on main.

❗ Current head 1cf319c differs from pull request most recent head 46fa685

Please upload reports for the commit 46fa685 to get more accurate results.

Files	Patch %	Lines
miditok/midi_tokenizer.py	84.21%	3 Missing ⚠️
miditok/classes.py	81.81%	2 Missing ⚠️
miditok/tokenizations/mmm.py	77.77%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #173      +/-   ##
==========================================
- Coverage   90.46%   90.32%   -0.14%     
==========================================
  Files          35       35              
  Lines        5525     5530       +5     
==========================================
- Hits         4998     4995       -3     
- Misses        527      535       +8     

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