[Design] Refactor code deps org. for core data structures (trees, hashes, core types)

[hadjiszs]

This seems to be copied from pessimistic-proof-core's LocalExitTree, so I haven't reviewed in-depth the folder. This being said, I'm thinking we may want to refactor code some more to avoid duplication, and have pessimistic-proof-core probably import the types from here. However, it does mean that this crate would become as frozen as pessimistic-proof, because we don't want the pessimistic proof to change randomly.

In particular, i do think that with the recent huge increase in deps here, this could not reasonably be reused by pessimistic-proof-core. I guess the real dependency we'd want is aggchain-proof-core -> pessimistic-proof-core, but so long as it lives in the same cargo workspace as agglayer it'll be hard to do.

I guess this needs some input from other people, eg. @hadjiszs / @Freyskeyd?

Originally posted by @Ekleog-Polygon in #57 (comment)