[TASK] Improve dependency graph + workspace structure

[lazovicff]

1. Structure

We should have a workspace with the following structure:

• arkworks-benchmarks
• arkworks-circom-verifier
• arkworks-r1cs-circuits - which contains only the r1cs constraints version of our circuits + gadgets
• arkworks-setups - contains the higher level APIs for both R1CS and PLONK circuits
• arkworks-native-circuits - which contains only the native version of our gadgets
• arkworks-plonk-circuits
• arkworks-utils

2. Tools

Use cargo-workspaces for workspace publishing.

3. Dependency graph

1. arkworks-gadgets should not have dependency of arkworks-utils, except for testing.

2. Move PoseidonParameters, Sbox, PoseidonError (https://github.com/webb-tools/arkworks-gadgets/blob/master/arkworks-utils/src/poseidon/mod.rs) into the arkworks-native-circuits/poseidon directory.

   • Types related to the native version goes to arkworks-native-circuits.
   • r1cs constraints version for sbox goes to arkworks-r1cs-circuits, etc.

3. Modify utility functions for Poseidon to not return PoseidonParameters struct, but instead return tuple:

   (Vec<F>, Vec<Vec<F>>, u8, u8, u8, PoseidonSbox)

4. Move setup_params...(https://github.com/webb-tools/arkworks-gadgets/blob/master/arkworks-utils/src/utils/common.rs#L23) functions inside the native version of poseidon.

5. Elliptic curves should only be imported for testing, for all crates.

[lazovicff]

@drewstone Let me know what you think. We could also break arkworks-r1cs-circuits and arkworks-plonk-circuits into two parts: arkworks-[x]-circuits + arkworks-[x]-gadgets, and rename arkworks-native-circuits into arkworks-native-gadgets

[drewstone]

This looks good

[drewstone]

We would need updates to the documentation as well @filiplazovic. Perhaps we can add to this proper rust docs and start publishing this online.