Implement solomachine chain context

[soareschen]

Summary

The design of chain context in the new relayer architecture allow the relaying between Cosmos and non-Cosmos chains. The simplest non-Cosmos chain that we can implement is a solomachine chain.

The IBC solomachine spec is rather simple, and we can implement an in-memory solomachine in similar ways as informalsystems/hermes#2733.

Here is a rough overview of how the solomachine would be implemented:

• It holds an in-memory merkle store.
• It holds an in-memory private key.
• It implements OfaBaseChain.
• It processes incoming IBC packets through the send_messages method.
• It creates new IBC packets to be relayed through its own methods outside of the chain trait.
• It follows the IBC specification and stores the appropriate IBC data in the given merkle path.

In this issue, we will be focusing only on relaying between two solomachines. #31 tracks the remaining work required to support relaying between a Cosmos chain and a solomachine chain.

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[DaviRain-Su]

I suggest that the solomachine client context here implement an abstraction layer, so that I regard the near chain or solana chain as a solo machine client so that some content should not be a specific chain.