reward collector - ICA message unit tests

[sampocs]

• Split SwapRewardTokens and TransferRewardTokensHostToTrade into 2 functions each - with one of them being a function only responsible for building a message
• Added unit tests around each of these, with one to cover the message contents, and a different one to cover the ICA submission
• Added a couple unit test helpers

[ethan-stride]

Awesome! LGTM
Beautiful solution to being able to test the msg without any state being stored by the ICA submit -- this call structure should probably become our convention going forward. I left some suggestions to simply even further but they are mostly matters of taste we can discuss.