Add `AtomMappingScorer` class

[atravitz]

Is your feature request related to a problem? Please describe.
AtomMappingScorer is implemented and used in Industry Benchmarks, konnektor, kartograf, and ruler: https://github.com/search?q=org%3AOpenFreeEnergy%20atommappingscorer&type=code

Describe the solution you'd like
This class should probably live in gufe, as expressed in #346. Though I believe we can add AtomMappingScorer before digging into the other items in PR#346.

Describe alternatives you've considered
We could define AtomMappingScorer directly in konnektor, but that's more code duplication.

[atravitz]

options include:

1. TypeAlias that allows us to have clearer documentation/static type checking, but is not a class.
2. make a class that inherits from Callable - this can avoid making users use functool.partial workarounds that are not friendly
3. make a class that has a method that is a Callable

In gufe dev meeting as of today, we (I) generally feel that:

1. easiest, already implemented in konnektor
2. maybe the best solution for handing more complex scorers, but maybe a 2.0 implementation
3. my least favorite option because it would break the API most and add a level of complexity