QuAM state gets prepended "q", even for string naming

[maxzanner]

When creating a QuAM state or wiring the qubit names have a prepended "q". The naming is created in element.py in the QubitReference and QubitPairReference classes. It is probably useful to prepend a "q" when someone uses a list of integers to create qubit names but in case of strings it should not be prependend.

Suggested fix:
return f"q{self.index}" --> return self.index if isinstance(self.index, str) else f"q{self.index}"