Support subclass fields in dataclass_array_container

[alexfikl]

get_annotations only gets annotations from the current class, but not from any subclasses. This extends that by going through the MRO (in reverse) and gathering all of them up.

Context: boxtree.Tree inherits from boxtree.TreeOfBoxes and this wouldn't recognize the fields from TreeOfBoxes, which are still in the list returned by fields(Tree).

[inducer]

Thanks! Added a test of sorts, plus some other coincidental typing stuff.

[alexfikl]

Thanks! Added a test of sorts, plus some other coincidental typing stuff.

Thanks for adding the test!