Error gen projection basis must be Basis object

[pcwysoc]

Describe the bug
Error generator projections require a Basis object and do not work with a basis name, i.e. 'pp'. This is not the expect behavior as listed in the documentation. The issue appears to be with how the errorgen_and_projections function in reportables.py handles basis information.

Environment (please complete the following information):

• pyGSTi version feature-qiskit-mcm
• python version 3.10
• OS Ventura 13.6.7

[sserita]

This should be an easy fix, mx_basis needs a Basis.cast(mx_basis) prior accessing .name or something similar. We'll probs need to infer the dimension from the incoming errgen matrix.