`NamedArray.shape` does not support unknown dimensions

[headtr1ck]

What is your issue?

According to the array api standard, the shape property returns tuple[int | None, ...].
Currently we only support tuple[int, ...]

This will actually raise some errors if a duckarray actually returns some None.
E.g. NamedArray.size will fail.

(On a side note: dask arrays actually use NaN instead of None for some reason.... Only advantage of this is that NamedArray.size will actually also return NaN instead of raising...)

[TomNicholas]

(On a side note: dask arrays actually use NaN instead of None for some reason.... Only advantage of this is that NamedArray.size will actually also return NaN instead of raising...)

Linking to more info on this, and the connection to ragged arrays: #4285 (comment)

also xref #5168, #2801