Make simc able to generate arguments and witness generation code

[schoen]

Project

compiler

Describe the feature

Per a suggestion from @KyrylR, the SimplicityHL compiler should be able to generate Rust and/or other language code like the argument and witness generators in, for example

https://github.com/BlockstreamResearch/simplicity-contracts/tree/main/crates/contracts/src/options

This is likely to be inferrable from type annotations on witness fields in the SimplicityHL program, although it would be much easier (and more powerful) in SimplicityNG. I think the basic idea is that we enumerate all standard-looking references to saved state and witness fields in the SimplicityHL program, and then emit boilerplate code that could create the corresponding data structures based on how those references are annotated or used inside the SimplicityHL. @KyrylR can correct or clarify this.

This is relevant to wallet and app integration, and, in some settings, to obviating the need to make .wit files on disk.

[Arvolear]

I'd not generate Rust code by the compiler itself. If we could get away with a simple json, that would be enough for a development framework to parse such files and a) take control over the development flow, b) provide more specific and user-friendly typization.