@Override
	public String toString() {
		return stack + ":" + treeStack + ":" + buffer + " (" + pos + ")";
	}
Look for previous machine states having the same stack and position

<p>
This would imply we have gone in a loop without consuming anything. We need to prune.

@param machine the machine state to check
@param visited the stack of previous machine states
@return if there is a loop, the machine state proving it, null otherwise
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/app/plugin/assembler/sleigh/parse/AssemblyParseMachine.java