Set minimum attrs version

[max-radin]

I found that upgrading attrs to 23.2.0 or higher would resolve errors such as

  File "/Users/maxradin/anaconda3/lib/python3.11/functools.py", line 994, in __get__
    raise TypeError(msg) from None
TypeError: No '__dict__' attribute on 'CtrlSpec' instance to cache 'shapes' property.

when using qualtran. (See isi-usc-edu/pyLIQTR#35 for example code and full traceback.)

My guess is that this is because earlier versions of attrs did not support cached properties on slotted classes, as described in python-attrs/attrs#1200. I'd suggest updating qualtran's requirements to specify a minimum version of 23.2.0 for attrs.