Adding updates to composite router and scaffolding for LegacyIBCModule

[chatton]

Description

This PR applies some PoC router changes to the feature branch.

The main idea being introduced is the concept of a ClassicIBCModule which will be the same as the IBCModule we have now, and then in a future PR we will strip down the IBCModule to no longer include the handshake fns.

In the channel handshake fns, we will route to the Classic modules, and in Send / Recv etc will will route to the slimmer IBCModule modules.

There is a bit of a hack introduced in the AddRoute function which gradually builds up the LegacyIBCModule based on consecutive calls to AddRoute. I think we should be able to remove this entirely with a single call to AddClassicRoute.

closes: #XXXX

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