makes AtomMappers subclass from GufeTokenizable (#266)

Co-authored-by: Irfan Alibay <IAlibay@users.noreply.github.com>

gufe/mapping/atom_mapper.py

@@ -4,10 +4,11 @@
 from collections.abc import Iterator
 import gufe
 
+from ..tokenization import GufeTokenizable
 from .atom_mapping import AtomMapping
 
 
-class AtomMapper(abc.ABC):
+class AtomMapper(GufeTokenizable):
     """A class for manufacturing mappings"""
     @abc.abstractmethod
     def suggest_mappings(self, A: gufe.Component,