Expand automated testing

[ben-denham]

Increase test coverage in the following areas:

• E2E tests: Enum parameters
• E2E tests: uncaching tasks
• E2E tests: handling task failures
• E2E tests: handling keyboard interrupts
• E2E tests: mlflow integration
• E2E tests: FsspecStorage
• Unit tests: TaskCoordinator/TaskState
• Unit tests: serialization.py
• Unit tests: LocalStorage
• Unit tests: FsspecStorage
• Unit tests: cache.py