* Make jumps, logic, and syscalls read from/write to memory columns
* Change CTL convention (outputs precede inputs)
* Change convention so outputs follow inputs in memory channel order
I was thinking we could have two sets of shared columns:
- First, a set of "core" columns which would contain instruction decoding registers during an execution cycle, or some counter data during a kernel bootloading cycle.
- Second, a set of "general" columns which would be more general-purpose. For now it could contain "looking" columns for most CTLs (Keccak, arithmetic and logic; NOT memory since memory can be used simultaneously with the others). It could potentially be reused for other things too, such as the registers used for `EQ` and `IS_ZERO` (but I know it's nontrivial to share those since we would need to use lower-degree constraints, so I wouldn't bother for now).
This PR implements just the latter. If it looks good I'll proceed with the former afterward.
It seems redundant in most contexts, e.g. `use plonky2::field::extension_field::Extendable;`. One could import `extension_field`, but it's not that common in Rust, and `field::extension` is now about as short.
