[Bug]: Fix failing benchmarks

[BradyPlanden]

Python Version

3.12

Describe the bug

Benchmarks are failing due to the API change to the BaseProblem class in #425. This should be a quick fix, but fast benchmarks should be run on the pull request CI to catch this in advance. We should be able to do this with the `--quick' argument for asv.

Steps to reproduce the behaviour

https://github.com/pybop-team/PyBOP/actions/runs/10302233827/job/28515461543

Relevant log output

No response