[WIP] feat: Powdr Support

[CeciliaZ030]

Todos:

• Raiko host & guest skeleton
• Design PowdrContext i.e. user args for Powdr proofs
• Implement prepare_input for Powdr guest, depending on what Powdr ZKP needs.
• Port Powdr proof pipeline in raiko-guest-powdr

raiko-guest-powdr Proof Generation

• bootstrap to compile Rust -> RISC-V -> Powdr asm (-> Pil), cache the .asm (or .pil) file

https://github.com/powdr-labs/powdr/blob/2f9dc9d3707b8166d27b75f1fa531c5a034bf28f/riscv/tests/riscv.rs#L230

• collect execution trace from asm or pil level (which one's faster?)

https://github.com/powdr-labs/powdr/blob/54045fbcf7e6bead68596fd79b5d63cce4dded1b/riscv/tests/common/mod.rs#L17

• generate proof with Halo2 (or others ...)

https://github.com/powdr-labs/powdr/blob/50d08cd5a733c4be5180f10b1e13553f8fc74b21/compiler/src/test_util.rs#L66