On-disk module cache

[Stebalien]

At the moment, we have no support for on-disk module caching. Wasmtime has built-in support for this but:

1. It's global (system wide).
2. It compresses modules. We end up spending a lot of time decompressing modules at runtime.

Now that we have an in-memory cache (inside the engine), we should add support for persisting this cache to disk. The first use-case will be speeding up conformance tests in CI by caching built modules in github actions.

[Jacarte]

I have some numbers regarding the second point.
During our fuzzing experiments, we collect some execution times. We execute several times (to get a distribution) each binary, executing from scratch every time. The speeding up on wasmtime compiling step (

ref-fvm/fvm/src/machine/engine.rs

Line 314 in ad06522

let module = Module::from_binary(&self.0.engine, wasm.as_slice())?;

) is about x16 when the wasmtime cache is enabled.

More on this soon

[Stebalien]

We will build this if/when we need it.