GPO only returns integer values for parameters when given integer constraints

**Description of the error**
If a parameter is given constraints which are both integers, a GPO optimizer will only consider integer values for that parameter, even if it is given a float initial value
**Describe the expected result**
GPO would return a float value for the parameter no matter the type of the constraints

**Describe the actual result**
GPO returns only integer values for the parameter

**Suggested fix**
Cast all constraints to float before optimisation

**Additional details**