Follow-up on message processor (handler) implementations

[adizere]

Summary of Bug

As a follow-up to #127, the short term plan for maturing the handlers is sketched below, in the order of their priority.

• Wrap-up the work for ICS03 - Connection handshake #127 (PR ICS3 connection handshake protocol (message processing logic) informalsystems/hermes#188) as soon as possible
  (Anca, Romain, Adi)
• Align testing across the handlers of ICS02 and ICS03; tentative strategy: test process as well as keep separately, then test dispatch by comparing its output to the ones of process and keep.
  (primarily Romain) -> deferred to Cleaner context mocks (testing infrastructure for modules) #111
• Adapt handlers to newer protobuf definitions, which include client state in the Try message
  (primarily Anca) -- Migrate handlers to newer protobuf definitions informalsystems/hermes#226
• Extend ICS02 client mock to permit multiple consensus states, and two client states, thus reflecting more realistic testing scenarios
  (primarily Adi) -- Extend client context mock to support more realistic unit testing #114
• Cleanup Any* related code
  (Romain) -- Cleanup Any* wrappers related code informalsystems/hermes#225
• Finish all ICS03 messages: Ack and Confirm left (Adi) -- ICS03 Ack and Confirm message processors informalsystems/hermes#223
• Finish all ICS02/ ICS07/ mock message processing (ICS02 done with Mock testing for ICS 18 (relayer) update client messages informalsystems/hermes#270, ICS07 deferred to later)
• Investigate whether we can replace TryFromRaw with the more standard TryFrom, with the goal of removing the former, see e.g., ICS 03 msgs.rs
  (Adi) -- this was made obsolete by Greg's Removed TryFromRaw, implemented DomainType where needed informalsystems/hermes#252

We'll expand and document each point (except for the first one) in a separate full-fledged issue as needed.

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