MNT: refactor find-replace path datatype

[tangkong]

          You might consider making helper classes here to represent attribute access, list indexing, dictionary key grabbing, etc. Super high-level thing that may not apply, but the general thought is:

AttributeItem(child, attr)
ListItem(child, idx).__repr__ = f"{child.name}[{self.idx}"]"
DictKeyItem(child, key).__repr__ = f"{child.name}[{self.key}]"

You have a chain of these that gives you a direct path to the object in question

Then you don't have to worry about passing around special strings and you lock down the expected items coming out of this, etc

Originally posted by @klauer in #198 (comment)