Batch-testing for specific errors

Instead of only having "non-compiling" and "compiling" folders, we could have "flow-error" folder, "type-error" folders, and assert for specific errors

The issue does not name files, tests, or entry points. Start by locating the existing "non-compiling" and "compiling" test folders, then determine how flow errors and type errors are currently classified and asserted. Done means the test organization supports those error categories and checks specific errors, but the desired error cases are not defined here.

Written by the indexing model from the issue text.