add support for arbitrary number of arrays per wafer in mnms sims

[xzackli]

Add support for a single wafer, i.e.

arrays_dr6 = ["pa6_f090"]
soapack_arrays_dr6 = ["pa6a"]
wafers_dr6 = {"pa6": ["pa6a"]}

Previously things were hard-coded for having pairs of arrays on each wafer.