Move the generic call circuit, witness, and library over from `anoma/anomapay-backend-multichain`

[heueristik]

Context

Currently, all circuits (token transfer, token transfer v2, trivial logic) are located in https://github.com/anoma/anomapay-backend-multichain.

The new generic call circuit prototype is more general than just AnomaPay and it should be moved in its own repository, also to be able to separately audit it from all the backend code in the future. Maybe the other circuits can be moved as well at a later point. This would allow to selectively open-source the circuits.

Note

The associated GenericCallForwarder contract can be found here: https://github.com/anoma/generic-call-forwarder

Scope

Move the code

• generic_call_circuit,
• generic_call_library, and
• generic_call_witness

from the https://github.com/anoma/anomapay-backend-multichain/tree/feature/generic-call-resource branch into the new https://github.com/anoma/generic-call-resource repo.
Figure out how the backend could import the crate and how to handle the traits. Another difficulty might be how testing can be done without the backend infrastructure.

It should be possible to publish the repo as one or multiple crates.

Note

There is an integration test branch by @sug0 on top of https://github.com/anoma/anomapay-backend-multichain/tree/feature/generic-call-resource. It would be good if these tests can still work.

Definition of Done

The new repo works and is imported in the backend. Importing it as git dependency is ok for now since this is a prototype and we don't have to publish a crate yet. It is also acceptable to release an 1.0.0-alpha.0 version or similar on crates.io.