Make PyROS `UncertaintySet` Valid Numeric Types Mutable

[shermanjasonaf]

Summary

Based on this comment in #2488, the set of acceptable types for any numeric entry of a PyROS UncertaintySet attribute is frozen whenever contrib.pyros is imported. As the set of acceptable types is based on core.expr.numvalue.native_numeric_types, itself a mutable object, we wish to allow the set of acceptable types to be mutable, while also improving the computational performance of PyROS UncertaintySet subclass attribute type validation routines.