Warnings when deployed gateway, voting verifier, and multisig prover contracts

[Olanetsoft]

... from devnet-amplifier.json using the Cosmwasm rust-optimizer.

warning: unused import: `axelar_wasm_std::VerificationStatus`
 --> contracts/aggregate-verifier/src/msg.rs:1:5
  |
1 | use axelar_wasm_std::VerificationStatus;
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

warning: `aggregate-verifier` (lib) generated 1 warning (run `cargo fix --lib -p aggregate-verifier` to apply 1 suggestion)
    Finished release [optimized] target(s) in 5m 47s

warning: unused import: `multisig::worker_set::WorkerSet`
 --> contracts/monitoring/src/msg.rs:4:5
  |
4 | use multisig::worker_set::WorkerSet;
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default
  

  warning: unused import: `axelar_wasm_std::VerificationStatus`
 --> contracts/aggregate-verifier/src/msg.rs:1:5
  |
1 | use axelar_wasm_std::VerificationStatus;
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

warning: `aggregate-verifier` (lib) generated 1 warning (run `cargo fix --lib -p aggregate-verifier` to apply 1 suggestion)

[cgorenflo]

unfortunately, the rust compiler isn't aware that these imports are actually needed for an attribute macro in those files, it's a false positive. These warnings can be ignored, we are thinking about the best way to get rid of them.

[ffe9f8]

Add to error messages doc