Ecall demo with Keccak-f

[naure]

Trace generation

• Expand StepRecord to support multiple accesses to registers and memory (beyond standard instructions).
• Introduce a module for syscall witness generation. See fn handle_syscall(…)
• Witness generation for Keccak-f. Same format as sp1.
• Runtime wrapper function syscall_keccak_permute.
• Test program using Keccak-f and concrete values.

Circuit part (standalone diff here)

There is a placeholder for upcoming precompile circuits. The real implementation must have the same effects as this one (same memory writes, etc).

• LargeEcallDummy is an extension of the dummy circuit to support precompiles.
• Support any number of registers and memory accesses.
• New testing technique using the real trace generator instead of artificial StepRecord’s. See keccak_step.

[matthiasgoergens]

Looks good overall, please see comments.

[naure]

@kunxian-xia Merged all recent changes, ready for review.