fix: shift type definitions to stub file

- typing uses ParamSpec whis is supported for Python 3.10+

Author: aleneum

transitions/experimental/decoration.py

@@ -1,8 +1,3 @@
-from typing import Callable, ParamSpec
-
-P = ParamSpec("P")
-
-
-def expect_override(func: Callable[P, bool | None]) -> Callable[P, bool | None]:
+def expect_override(func):
     setattr(func, "expect_override", True)
     return func

transitions/experimental/decoration.pyi

@@ -0,0 +1,6 @@
+from typing import Callable, ParamSpec
+
+P = ParamSpec("P")
+
+
+def expect_override(func: Callable[P, bool | None]) -> Callable[P, bool | None]: ...