Update Scenario Mining Evaluation

[CainanD]

PR Summary

• Updated scenario mining evaluation to support submissions that do not contain tracking predictions
• Parallelized tracking threshold calculation for 3x speedup
• All metrics are now averaged across class rather than averaged across instance
• Made variable names more consistent

Testing

Tested using scenario mining unit tests. It is also confirmed to work with the new EvalAI leaderboard.

In order to ensure this PR works as intended, it is:

• [yes] unit tested.
• other or not applicable (additional detail/rationale required)

Compliance with Standards

As the author, I certify that this PR conforms to the following standards:

• [yes] Code changes conform to PEP8 and docstrings conform to the Google Python style guide.
• [yes] A well-written summary explains what was done and why it was done.
• [yes] The PR is adequately tested and the testing details and links to external results are included.