Move the Constants/Arithmetic/Bitwise/Comparisons/Logical opcode handler
bodies out of emitInst into a new Ops facade in src/backend/llvm/ops.zig.
emitInst's scalar arms now delegate via self.ops().*; the shared infra they
call (mapRef/resolveRef/matchBinOpTypes/emitCmp/emitCmpOrdered/emitStrCmp/
emitStringConstant/reflection + isFloatOrVecFloat/isSignedType) stays on
LLVMEmitter, widened to pub as needed. Pure relocation: zero snapshot churn.