Add slots to the StateMachine class

[bdraco]

Proposed change

Add slots to the StateMachine class

Fixes all tests to avoid patching the state machine.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

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• This PR fixes or closes issue: fixes #
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[bdraco]

We could do the same for the event bus if we can get rid of all the legacy tests that patch core

[MartinHjelmare]

What's the benefit with slots here?

[bdraco]

Usually it's for memory, but slotted classes also have faster attribute lookups since they don't have the overhead of __dict__

[MartinHjelmare]

Thanks!

[bdraco]

Thanks