Multitrack ProgramChange

[Natooz]

Following #71, this PR adds the option (config.program_changes) to use Program tokens similarly to the way the MIDI Program Change messages occur.

The option only works for TSD, REMI and MIDILike as multi-voc tokenizers will gather the Program information with the note tokens, program changes would break Structured's recurrent token type succession, and MMM already separate the tracks within the token sequence.

Still a few things to check, and enforce the multitrack tests

[codecov]

Codecov Report

Patch coverage: 85.25% and project coverage change: +0.45% 🎉

Comparison is base (a1543cd) 89.21% compared to head (1c92383) 89.67%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #72      +/-   ##
==========================================
+ Coverage   89.21%   89.67%   +0.45%     
==========================================
  Files          31       31              
  Lines        4201     4260      +59     
==========================================
+ Hits         3748     3820      +72     
+ Misses        453      440      -13     

Files Changed	Coverage Δ
setup.py	0.00% <ø> (ø)
miditok/classes.py	84.50% <42.85%> (-3.96%)	⬇️
tests/test_one_track.py	78.33% <66.66%> (+6.16%)	⬆️
tests/tests_utils.py	77.35% <68.08%> (-4.06%)	⬇️
miditok/tokenizations/midi_like.py	93.75% <85.71%> (ø)
tests/test_multitrack.py	83.60% <88.23%> (+13.72%)	⬆️
miditok/midi_tokenizer.py	89.06% <97.77%> (+0.97%)	⬆️
miditok/constants.py	100.00% <100.00%> (ø)
miditok/tokenizations/cp_word.py	93.43% <100.00%> (+0.41%)	⬆️
miditok/tokenizations/mmm.py	92.34% <100.00%> (+0.03%)	⬆️
... and 7 more

... and 1 file with indirect coverage changes

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