ty currently adds tests as a search path if the user didn't specify any. This is problematic because it prevents ty from detecting test modules being imported into production code.

The main reason we added the fallback tests was to make imports work within the test folders. This is no longer required now that we have desperate module resolution.

We should try changing the default and see how big the fallout on mypy primer is. If it's small, I suggest landing this change before the beta.

We should also update ty's module resolution documentation to mention the new desperate module resolution algorithm.