Push parameter caching up to Collection?

[mattwthompson]

          Might it also make sense to generalize this caching code to the `Collection` class - perhaps have a `parameters: dict[TopologyKey | <etc>, Potential` property there? I imagine most of the cost of `_get_charges()` is the repeated dictionary lookups, though maybe having to do an attribute lookup would just reproduce that. `parameters: dict[TopologyKey | <etc>, tuple[int, ...]` would be a nicer, maybe faster API, but it would mean each collection would have to somehow define an ordered set of parameters. I'm not sure if that would be worthwhile.

Originally posted by @Yoshanuikabundi in #1115 (review)