Fix ID models

[gitttt-1234]

This PR fixes a few minor issues with TopDown and BottomUp ID models.

• The ID models dataset classes were re-computing the tracks from the labels file. However, they should just grab it from the head config classes parameter.
• Fix shape mismatch issue with BottomUp ID models

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.54%. Comparing base (ff91433) to head (3ef67a3).
⚠️ Report is 47 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #345      +/-   ##
==========================================
- Coverage   95.28%   93.54%   -1.74%     
==========================================
  Files          49       49              
  Lines        6765     7006     +241     
==========================================
+ Hits         6446     6554     +108     
- Misses        319      452     +133     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.