fix(python): complete some straightforward API annotations

[jonasdedden]

Summary

• correct Dict[str, any] to Dict[str, Any]
• parameterize public dictionaries and AbstractContextManager
• use the directly imported Arrow Expression type instead of an unresolved module attribute
• annotate variadic keyword arguments and the None return from create_scalar_index

[lance-gatekeeper]

✅ Gate recommendation: approve.

These corrections remove the demonstrated invalid and unresolved public annotation types while keeping the runtime API and import behavior unchanged. Keeping the annotations inline also avoids a second type-definition surface.