v0.10.0a4

Breaking Changes

• Assigning a state var through its state class, such as State.count = 10, raises TypeError instead of replacing the var; so do pytest's monkeypatch.setattr and unittest.mock.patch.object on a var. Change a default with State.__fields__["count"].default = 10, patch the field in tests, and declare class-level configuration as ClassVar. (#7516)