Unifying `instantiate2` implementation

Description

Our team at @AbstractSDK is working on refactoring our smart-account implementations to be optimized for account-abstraction use-cases. Because each user on the blockchain will have an Abstract smart-account created for them, we're trying to minimize the state that is stored under the contract's namespace.

The account needs to be aware of a few contracts in order to do verification of actions or call specific functionality on them.

Our Solution

To reduce the state we've been exploring the use of instantiate2 to deterministically compute the canonical address of each contract and include them in the WASM binary directly as bytes, to be humanized at runtime. As the # of Accounts scale, this should have a significant impact on the storage use of our solution.

To get the address of any of these native contracts we do the following:

Upload a CosmWasm "blob" contract that is a minimal CW contract.
Use instantiate2 with a contract-specific salt to claim the address for that specific contract.
Migrate the blob on that address to the contract that we want to have occupy that address.

The Problem

The problem that we're facing is that this workflow does not give us the same addresses in the cw-multi-test environment due to the fact that its instantiate2 method does not incorporate the actual checksum of the blob contract.

As a result we're forced to either:

Construct our own ChecksumGenerator and use it in all our cw-multi-test uses.
- We don't like this solution because as a development framework, we'd require all our users to use this exact ChecksumGenerator, which might conflict with their own requirements.
Use feature-flags to select a set of different addresses for use in cw-multi-test.
- This will create conflicts in our codebase, requiring us to separate cw-multi-test tests from all other kinds of tests and would create a lot of complexity in our codebase overall.

Discussed Solution

We've internally discussed an addition to cw-multi-test that would allow users to set the checksum of a contract through the Contract trait.

pub trait Contract<C, Q = Empty>
where
    C: CustomMsg,
    Q: CustomQuery,
{
    /// Get the checksum of the contract
    // Defaults to None (not API breaking)
    fn checksum(&self) -> AnyResult<Option<String>> {
        Ok(None)
   }
}

And then update ContractWrapper to contain an optional checksum value.

pub struct ContractWrapper<
   ...
> where
    ...
{
    // Add an optional checksum field
    checksum: Option<String>,
}

And update the instantiate2 method to use this checksum if Some.

Doing this would allow developers to use the exact same addresses for their contracts in a test environment as a wasmd environment without requiring custom checksum generators.

Questions

Is this an acceptable solution?

CosmWasm / cw-multi-test