make type checkers happy

[Catminusminus]

This PR will Fix #2 and some type errors.

The following three types of type errors are currently occurring:

• Caused by incomplete types.
  • This is the one pointed out in Incomplete type annotations lead to error diagnostics from static type checkers #2. Bare “Callable”s correspond to it.
• Due to covariance.
  • If A is a subtype of B, it seems natural that Option[A] is also a subtype of Option[B]. So we use T = TypeVar("T", covariant=True) for class Some(Generic[T]):. However, because covariant type variable cannot be used in parameter type, we cannot use def unwrap_or(self, default: T) -> T:.
• Due to Lack of runtime annotation
  • Think about Nothing().map(lambda x: x + 1). The problem is that the type of lambda x: x + 1 is not clear.
    It would be nice if we could annotate this lambda expression with the type directly, or annotate Nothing directly, but that is not possible (of course it is possible via a temporary variable, but Ruff does not allow lambdas to be put into temporary variables).

To address these issues, I did the followings:

• Eliminated incomplete types.
• Excluded T from the function arguments. In particular, I used Any instead.

[qexat]

it looks good to me!