Bugfix: Cast track id to int when loading from df

[cmalinmayor]

Proposed Change

Bugfix: Ensure the track ids are ints when loading from dataframe or csv.

Checklist

• I have added tests that prove that my feature works in various situations or tests the bugfix (if applicable).
• I have checked that the tests pass and I maintained or improved test coverage (if applicable).
• I have written docstrings and checked that they render correctly in the documentation build.