feat(arbitrum): light client (#1868)

- [x] add Arbitrum to `chain-utils`
- [x] add Arbitrum to `block-message`
- [x] add Arbitrum to `relay-message`
- [x] create proto definitions for light client
- [x] `arbitrum-verifier`
  - untested, will add testdata in followup pr
- [x] `arbitrum-light-client`
- [x] docs on how the light client and state tracking works
- do NOT let me merge this PR without this one checked off. I promise
you I will try
  - this is documented in `arbitrum.proto`

Other misc. changes made in this PR:
- implement `IntoIterator<Item = u8>` for byte array wrapper types
directly
- tracing improvements
- a few ICEs for good measure
- start exposing useful fetching actions via the cli (query latest
height) both generically and for specific chains
- add chain id to all voyager logs (where applicable)
- clean up error types in `ethereum-verifier` and `arbitrum-verifier`
(print full error stack since cosmwasm doesn't call `.source()` on the
error type, it just uses `Display`)
- devnet-union proposal period is now 30 seconds, not 2 days