Get rid of mypy's # type: ignore[unreachable] comments

[Saransh-cpp]

Right now mypy throws a bunch of errors in this particular code block -

vector/src/vector/backends/awkward.py

Lines 575 to 582 in 02d4655

	def _class_to_name(cls: typing.Type[VectorProtocol]) -> str:
	if issubclass(cls, Momentum):
	if issubclass(cls, Vector2D): # type: ignore[unreachable]
	return "Momentum2D" # type: ignore[unreachable]
	elif issubclass(cls, Vector3D): # type: ignore[unreachable]
	return "Momentum3D" # type: ignore[unreachable]
	elif issubclass(cls, Vector4D): # type: ignore[unreachable]
	return "Momentum4D" # type: ignore[unreachable]

saying -

error: Subclass of "VectorProtocol", "Momentum", and "Vector2D" cannot exist: would have inconsistent method resolution order  [unreachable]

These errors have been suppressed using the type: ignore[unreachable] comments, but this should be fixed. The type: ignore[unreachable] comments should be removed from Vector (these are the only type: ignore[unreachable] comments left in the codebase).

---

Guessing it is not understanding that Type[VectorProtocol] can (sometimes) pass a subclass of Momentum check? Might be worth updating that. But not in this PR, these are (all) fine for now.

Originally posted by @henryiii in #219 (comment)

[Saransh-cpp]

#89 removes warn_unreachable = true for now.

[Saswatsusmoy]

I guess the issue here is that Momentum is a subclass of VectorProtocol, while Vector2D, Vector3D etc. are also subclasses.