Verifying register values in syscall read preimage

[dannywillems]

          For a follow-up, but still important to write a proper test: we might want to add a check that some registers have been set correctly for the whole execution, after each call to the instruction.

Many "virtual" registers are written in request_preimage_write.

Originally posted by @dannywillems in https://github.com/o1-labs/proof-systems/pull/2305#discussion_r1643003090