Consider guaranteeing that iteration over BiocPy objects should be hashable

[LTLA]

This makes writing generics a lot easier because we can safely iterate across objects, so things like factorize() and match() would just work correctly.

For example, currently BiocFrame iteration produces a dict, which is not hashable. (Incidentally, BiocFrame iteration also includes the row names in the tuple, and it probably doesn't need to, as the row names are optional.)

[LTLA]

I suppose iteration of a GRL returns a GR, which probably isn't hashable in general. Maybe we need a dedicated hashable_iterator() generic to represent this concept.

[LTLA]

Oh, and sortable, then something like order() would also work.

[LTLA]

Actually, before we get too into it, we should probably just try to turn all the verbs into generics and see how hard they are to implement in more complex containers. See the overview of verbs at ?"xtfrm,Vector-method" from S4Vectors, which underlies generic methods like sort, unique, and match.