[WIP] feat: add zicond operations

[tobiasgrosser]

We add the zicond operations: https://docs.riscv.org/reference/isa/unpriv/zicond.html

The Sail monad for zicond reads both register values depending on the value of the first register read. In the operation
if val2 = then 0 else val1, the register containing val1 is only read if it's actually used (i.e., val2 = 0). We obviously can't represent this behaviour in the pure semantics and therefore had to (1) rely on batteries for the manipulation of monads (2) build some more infrastructure around the reading and writing of registers.

All this infrastructure lives in ForMathlib.

Co-authored-by: Sarah Kuhn kuhnsa@student.ethz.ch