Split out Cosmos-specific code into its own crate

[romac]

Crate

ibc-relayer

Summary

Split out the CosmosSdk struct, its ChainEndpoint implementation, and all related Cosmos-specific code into a ibc-relayer-cosmos crate.

Problem Definition

While the relayer was developed against and currently only supports Cosmos chains, this will have to change in the future with non-Cosmos chains connecting via IBC. Because it is likely that each and every non-Cosmos chain will require specific support and tailored code in the relayer, the ibc-relayer library will grow in size and in scope way past a healthy point for a library.

Proposal

Split out all the Cosmos-specific code out of the ibc-relayer crate and into a new ibc-relayer-cosmos crate.

Code to split out

TBD

Acceptance Criteria

The ibc-relayer crate does not contain any Cosmos-specific code and a new ibc-relayer-cosmos crate is added to the workspace.

Potential concerns

• Cyclic dependencies between ibc-relayer and ibc-relayer-cosmos, may require introducing a ibc-relayer-base crate or similar to host the traits to be implemented in the -cosmos crate.

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[mzabaluev]

Cyclic dependencies between ibc-relayer and ibc-relayer-cosmos

This can be avoided if the entry API for setting up a Cosmos relayer is made public in ibc-relayer-cosmos, and ibs-relayer is a base library agnostic of specific chains.