[uss_qualifier] rename and generalize VerticesResource to VolumeResource

[Shastick]

First step towards #1053:

Rename VerticesResource to VolumeSpecification and let it have a single field of type Volume4DTemplate, which will allow us to use the optional (and dynamic) time-bounds out of the box.

This PR does not yet update scenarios to make usage of the dynamic time-bounds, this will happen in a follow-up PR.

[BenjaminPelletier]

This operation should apply to an outline; probably a Volume3D if we want to make it easier to support non-polygonal shapes like circles in the future. We don't want to put a method on a high-level object that operates only on a much narrower subcomponent because that reduces reusability for other things that use only the narrower subcomponent (e.g., if we later wanted S2 vertices from a Volume3D for some other reason, we would be likely to duplicate this logic since it's not obvious we should go looking in a much higher-level special-purpose VolumeSpecification for that existing code).

We can add convenience accessors to higher-level objects, but we should make sure the actual operation is always performed at the appropriate lower level. An accessor would probably look something like:

def s2_vertices(self) -> list[s2sphere.LatLng]:
    return self.template.resolve({}).volume.s2_vertices()

with

class Volume3D(ImplicitDict):
    def s2_vertices(self) -> list[s2sphere.LatLng]:
        [the rough implementation shown here]

Plus, the implementation here isn't even correct because a Volume4DTemplate includes, for instance, transformations.

[Shastick]

Switched to using resolve() and moved the logic for s2_vertices to Volume3D

[Shastick]

Bumped the minor number given that the change is breaking.