Factor out test_symbols_isolated real db system to the rest of the tests

[carkod]

In PR #804 we've created a new system for testing using mocks. Instead of using mocked functions, we want to use real data, stored in SQLlite and use that freezed data as mocks.

This task should be carried out with Copilot, as it's mostly test migration, logic should not change.

This follows the VCR practice of using real data, rather than useless fake mocks. VCR records third party requests, not database operations, so we had to create our own.