Refactor list of RPC methods to test

[seancolsen]

This PR cleans up the code in test_endpoints.py so that it's easier to add new RPC methods to that file.

This is its own PR because:

1. It would be nice to get this merged soon so that we can all work on top of it.
2. I ran into some weird test failures that I want help troubleshooting in isolation.

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[seancolsen]

@mathemancer or @Anish9901 could you look at this and help me troubleshoot the test failure?

These both work:

docker exec mathesar_service_dev pytest -k test_rpc_endpoint_expected_methods

docker exec mathesar_service_dev pytest -k test_correctly_exposed

But when the tests are run together this fails:

docker exec mathesar_service_dev pytest mathesar/tests/rpc/test_endpoints.py

I don't understand what's going on. I can continue troubleshooting on my own if you're confused too. But I figured one of you might have a quick guess as to the cause.

[seancolsen]

Came back to check on this... Now I see that the tests are passing in CI. Weird. 🤷‍♂️ 😬

[mathemancer]

Came back to check on this... Now I see that the tests are passing in CI. Weird. 🤷‍♂️ 😬

Long story short, the Django test DB setup doesn't play nicely with test parallelization. So, in CI, we just run the failed tests until everything is passing, or until some test fails 5 times. This, along with the parallelization, is faster than running the tests serially.

As we progress to the portion of the refactor where we're removing vast swathes of code, and associated tests, I want to move these back to running serially, and eventually we should only need the Django test DB setup quite rarely (e.g., for E2E testing).

For now, just re-run with the --lf flag, and only believe failing tests if they fail multiple times.