Add untested/unintegrated nomad-substrate crate

[luketchang]

Motivation

Enable Nomad agents to run against substrate chains. Must add nomad-substrate crate to implement contract traits.

Solution

Major High Level Changes

• Adds nomad-substrate crate to rust/chains but does NOT integrate into rest of codebase (i.e. nomad-base and agents)
• Moves nomad_core::ChainCommunicationError to nomad-base and makes it a wrapper across chain-specific error types defined in `chains
  • Note that this solves the issue of having chain-specific errors leak into nomad-core
  • Note this is also consistent with having nomad-base draw on chain-specific crates and serve as chain-agnostic wrapper
• Changes nomad_core::{Common, Home, ConnectionManager} to return associated type error (Self::Error), having chain-specific crates define/return their own chain-specific error types (e.g. EthereumError, SubstrateError)

Details

• nomad-substrate
  • Adds SubstrateHome and SubstrateHomeIndexer objects and implements necessary nomad_core traits
  • Adds SubstrateError type which wraps all subxt and scale-value deserialization errors (substrate-specific)
• nomad-core
  • Removes ChainCommunicationError (changed/moved to nomad-base)
  • Has contract traits return associated type errors instead of the old ChainCommunicationError
• nomad-base
  • Adds new ChainCommunicationError which wraps nomad_ethereum::EthereumError and nomad_substrate::SubstrateError
• nomad-ethereum
  • Adds EthereumError error enum to wrapper ethers and gelato errors (ethereum-specific)
  • Has existing contract methods return Results<_, EthereumError> now instead of using old ChainCommunicationError
• accumulator
  • Adds deserialization for LightMerkle (nomad-substrate needs this to decode tree object)

PR Checklist

• Added Tests
• Updated Documentation
• Updated CHANGELOG.md for the appropriate package
• Ran PR in local/dev/staging

[luketchang]

Closing in favor of #232