TYP: create and use `ArrayNamespace` type alias

[lucascolley]

Throughout the codebase we annotate array namespace parameters (usually called xp) as ModuleType. We hope to narrow this type to something like ArrayNamespace when a protocol is developed in https://github.com/data-apis/array-api-typing.

For now, it would be good to add an ArrayNamespace = ModuleType alias at

array-api-extra/src/array_api_extra/_lib/_utils/_typing.py

Lines 5 to 8 in 48fb66a

	# To be changed to a Protocol later (see data-apis/array-api#589)
	Array = Any # type: ignore[no-any-explicit]
	Device = Any # type: ignore[no-any-explicit]
	Index = Any # type: ignore[no-any-explicit]

and use it throughout the codebase.