Future: Standardize TrackStatus data type

[Casper-Guo]

According to SCHEMA.md, the TrackStatus column should be int type. In reality, it is a mix of int and float type. This has not caused any issue yet because the data is standardized in visualization.py via _correct_dtype before it is used anywhere.

Todos:

• Rewrite preprocessing pipeline so TrackStatus is always int
• Reprocess existing data
• Update _correct_dtype to reflect the change