allow _create_durations_tuples to be overriden, and new tokenizer loading logic

[JLenzy]

1. Allow _create_durations_tuples function to be overriden, thus allowing for more flexible creation of time events in new tokenization methods
2. Tokenizer base class can now call _load_params with a dictionary (not just a .json file path). This allows for more fluid integration into model saving/loading functions as it doesn't require a file to be written/read when loading the tokenizer.

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📚 Documentation preview 📚: https://miditok--152.org.readthedocs.build/en/152/

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 90.85%. Comparing base (a1ce1e7) to head (fd538b4).

Files	Patch %	Lines
miditok/midi_tokenizer.py	85.71%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #152 +/- ## ========================================== - Coverage 91.18% 90.85% -0.34% ========================================== Files 33 33 Lines 4994 4996 +2 ========================================== - Hits 4554 4539 -15 - Misses 440 457 +17 ```

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