@PcodeUserop
	public Pair<byte[], TaintVec> taint_var(Pair<byte[], TaintVec> in) {
		return Pair.of(in.getLeft(), in.getRight().eachUnion(nextVar()));
	}
Taint the given machine variable with a single taint symbol

<p>
This generates a single taint symbol (mark), places it in a singleton set, and then broadcast
unions it with the taint vector already on the input variable. For example, assuming an
initial state with no taints, the Sleigh code {@code RAX = taint_var(RAX)} will cause every
byte of RAX to be tainted with "var_0".

@param in the input value
@return the same value, with the generated taint unioned in
Ghidra/Debug/TaintAnalysis/src/main/java/ghidra/pcode/emu/taint/TaintPcodeUseropLibrary.java