Add _editor: str | None = None to the class-level attribute declarations #27

The _editor attribute is initialized in __post_init__ but not declared as a class-level attribute in the dataclass. This could lead to inconsistent behavior with static type checkers and IDEs. Add _editor: str | None = None to the class-level attribute declarations (around line 23-27).

Originally posted by @Copilot in #22 (comment)