Demo precompile as firmware.

[naure]

Implement some precompile or ecall as regular software written in Rust and loaded into the VM; hence the name firmware. The VM implements such precompile calls as jumps to the literally precompiled RiscV code.

This enables us to increase compatiblility with existing platforms like sp1 before (or without) circuit implementations.

[matthiasgoergens]

Please add some motivation for why we would want to do this.