Rewrite and/or drop policy search test

[anth-volk]

This test has repeatedly been the cause of spurious errors, mainly because it tests against a local database run instead of mocking the db altogether. This leads to a race condition anytime that tests are run simultaneously, since all tests are being run against the same db.

[anth-volk]

E.g., this is occurring in the run at https://github.com/PolicyEngine/policyengine-api/actions/runs/12015833593/job/33494726478, since three other runs occurred at almost the same time due to changes being pushed close together.