refactor(unionlabs): clean up ics24 (previously proof) module (#1675)

closes #1673

After some internal discussion, I think it's best to keep this module in
`unionlabs`, to avoid over-fragmenting our codebase; however the module
rename is still good.

- `unionlabs::proof` -> `unionlabs::ics24`
- added the remaining paths (receipts and next sequence paths)
- implementations in `chain_utils::ethereum` are stubbed out for now,
until #1663 is resolved
- simple proc macro for generating the `Display` and `FromStr`
implementations
  - much nicer to look at the module now lol
  - also one less use site of `derive_more`
- removed the `Path` suffix from the `Path` enum variants
- `IbcPath::Output` -> `IbcPath::Value`
- `Output` is just my default associated type name, `Value` is clearer
(although still not great, open to suggestions)