Allow GenArchVals functions to indicate an error.

[kquick]

Currently, the lookupReg and updateReg function stored in GenArchValues are defined as pure functions, but it could legitimately return an error to the caller under certain conditions (e.g. being passed an invalid register value). This forces architecture-specific code to use error or panic (see the implementation for macaw-symbolic-riscv) and makes the code partial. While the API cannot enforce valid values on the client side, it should be able to throw the error back to the offending code rather than halting the program.

macaw/symbolic/src/Data/Macaw/Symbolic.hs

Lines 290 to 296 in eb0a3c7

	, updateReg
	:: forall sym tp
	. (SymArchConstraints arch, IsSymInterface sym)
	=> C.RegEntry sym (CG.ArchRegStruct arch)
	-> M.ArchReg arch tp
	-> C.RegValue sym (PS.ToCrucibleType tp)
	-> C.RegEntry sym (CG.ArchRegStruct arch)