[Refactor Followup] Fix type errors in scheduler package

[jaredoconnell]

Summary and Details

This PR fixed type errors in the scheduler package. Many of them are Null errors and some are fixing type annotations on more complex types. One group of errors is switching the type annotations to reflect that the data structures are only storing string IDs instead of the type instances.

There is one remaining type error that can be found by running mypy on the scheduler folder. I believe that has to do with re-using the typing from the worker group in the singular worker. The problem is that SchedulerState is present in the group, but not the singular worker.

This PR removes 44 type errors, bringing the current count to 83.

Test Plan

I ran some basic benchmarks.

Run benchmarks to ensure the scheduler is still working as intended.

---

• "I certify that all code in this PR is my own, except as noted below."

Use of AI

• Includes AI-assisted code completion
• Includes code generated by an AI application
• Includes AI-generated tests (NOTE: AI written tests should have a docstring that includes ## WRITTEN BY AI ##)