Enhance multi test

[ethanfrey]

Make this compatible with more advanced workflows

• Support returning Response with custom message (this was a TODO)
• Add support for contract wrappers with sudo entrypoint

TODO (other PR?)

• Expose sudo on top level
• Add support for reply entry point
• Process submessages in app and pass response into reply

[ethanfrey]

I'm going to merge and tag this to unblock some work, and add the other items in a future PR.

[ethanfrey]

Okay, I made a 0.6.0-alpha2 release with this and got one step further. Now the issue is:

 --> contracts/tgrade-valset/src/contract.rs:423:40
    |
423 |         let valset_id = app.store_code(contract_valset());
    |                                        ^^^^^^^^^^^^^^^^^ expected struct `cosmwasm_std::Empty`, found enum `tgrade_bindings::TgradeMsg`
    |
    = note: expected struct `Box<(dyn Contract + 'static)>`
               found struct `Box<(dyn Contract<tgrade_bindings::TgradeMsg> + 'static)>`

So, I guess and app must accept only contracts that are Contract<C> with the same C. We assume there is only one custom message type on the chain, so in general this is good, but we must support Contract<Empty> as well.

So, basically, we will need to store &dyn Contract<C> in the app, but the contract wrapper should be able to accept functions that return Response<Empty> and convert it to Response<C> to handle this.