Fixing time signature preprocessing (time division mismatch)

[Natooz]

Fixes #131
In _preprocess_time_signatures, the ticks_per_bar computations were made based on the tokenizer's time division instead of the MIDI's, which can be different depending on the time signatures in the MIDI and those supported by the tokenizer, resulting in erroneously shifted time signatures.
Now the MIDI's time signature is passed to _preprocess_time_signatures .

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📚 Documentation preview 📚: https://miditok--132.org.readthedocs.build/en/132/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3cb6b97) 91.19% compared to head (7834595) 91.17%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #132      +/-   ##
==========================================
- Coverage   91.19%   91.17%   -0.03%     
==========================================
  Files          33       33              
  Lines        4886     4886              
==========================================
- Hits         4456     4455       -1     
- Misses        430      431       +1     

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