Prototype Athena VM support

[lrettig]

Here's a rough outline of how we might add Athena support to go-spacemesh:

1. Create a new vm module that implements the same interface as genvm
2. Rip out most of the code, including the template code. Add only a simple Wallet template for now, written in Rust and targeting Athena, that only implements send. Handle two transaction types: self_spawn and call. Get this running on a testnet. (I'm working on these first two now in Proof of concept Athena VM integration #6180)
3. Add the other missing methods to the Wallet template: call and deploy.
4. Add a spawn host function to Athena (spawn an existing template). Implement spawn in the Wallet template. Get this running on a testnet.
5. Add a deploy host function to Athena (deploy a new template). Implement deploy in the Wallet template. Get this running on a testnet. At this point, the testnet should allow users to deploy and spawn any code.
6. (additional stages related to rollup design and implementation, to be determined)

CC @poszu