In the add_client_assign_integer_variable factory, the variable lower and upper bounds are hard-coded to 0 and 1, respectively. This is correct for the $p$-median and $p$-center models. However in the CLSCP-SO formulation, there is no upper bound on the assignment variables (see equation [7.28] of Church & Murry 2018):
$$z_{ij} \geq 0$$
Moreover, in the CLSCP-SO the client assignment variables are not constrained to be integers, which we already account for by setting them as continuous.

So we need to either:

1. rename the method and add keywords for lower/upper bounds
   • add_client_assign_integer_variable -> add_client_assign_variable
2. create a new method
   • add_client_assign_continuous_variable

Choice (1.) is the most elegant and maintainable solution, IMHO.