Missing type hints causes mypy to complain

[jnewbigin]

Because of the missing type hints, when using cls=DefaultGroupit is necessary to use # type: ignore to prevent errors like:

error: Untyped decorator makes function "my_function" untyped  [misc]

So I copied the types from click 8.1.7 which makes mypy happy. I'll open the PR shortly.

[jnewbigin]

See #27 for possible resolution for this issue