[Bug]: SciPy Differential Evolution parallelisation broken

[BradyPlanden]

Python Version

3.12

Describe the bug

When trying to run SciPy Differential Evolution with parallel execution, there is a pickling error from the cost wrapper.

Steps to reproduce the behaviour

Running any example with SciPy Differential Evolution and workers arg set to > 1:

optim = pybop.SciPyDifferentialEvolution(
    cost,
    max_iterations=100,
    workers=-1
)

Relevant log output

    cls(buf, protocol).dump(obj)
AttributeError: Can't pickle local object 'SciPyDifferentialEvolution._run_optimiser.<locals>.cost_wrapper'

[BradyPlanden]

Here's the issue discussed on teams @PipGrylls