[BUG] failing tests on `main` in `test_efficient_cdar` and `test_efficient_semivariance`

A number of tests are currently failing on `main`. These should be investigated:

* `test_efficient_semivariance.py::test_efficient_risk_low_risk`
* `test_efficient_semivariance.py::test_max_quadratic_utility_range`
* `test_efficient_cdar.py::test_efficient_return_L2_reg`
* `test_efficient_cdar.py::test_efficient_risk_L2_reg`