ZIR-280: Keccak2 InitCycle is deterministic 🎉

[jacobdweightman]

I've written a bunch of code for Picus integration, and thought it would be good to open a PR at an intermediate step so it's not so ridiculously enormous. Summary of changes:

• Added "attribute" syntax for components, modeled after Rust attributes. Currently, the only supported attribute is picus:

#[picus]
component Foo(x: Val) {
  a := Reg(x);
}

• Added --emit=picus option which emits picus code for components with the picus attribute and their transitive dependencies
• Added scaffolding for Picus lowering, and implemented a medium-sized chunk of it
• Created a new InlineForPicusPass which inlines some components to improve Picus performance (Shankara's suggestion, and doubles as a stopgap for a missing Picus feature)

[mars-risc0]

I don't understand enough about picus to evaluate the system of signals being generated, but the compiler-side changes all make sense to me.

[mars-risc0]

Thank you for the tour through the codebase earlier; this all seems clear and reasonable, now that I understand what it is trying to do.