### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

Encountered this while running tests for another fix. On a fresh clone of the repo after `make bootstrap`, `make test-unit` stops at collection with three "import file mismatch" errors due to three pairs of test files sharing the same base name `test_models.py` `test_main.py` `test_streaming_iterator.py` whose directories aren't packages so pytest imports both halves of a pair as the same module and then aborts causing multiple tests to never run.

I don't think CI/CD caught this yet because the unit test workflows shard by directory so the pairs never end up in the same pytest session. `make test-unit` runs the whole tree in one session which is why it only shows up locally and it's the command in `CONTRIBUTING.md` we're told to run

The fix looks straightforward and small as parts of the tree already use `__init__.py` markers and adding them along the colliding chains resolves it.

I can open a PR to fix this. I've already written a fix, tested it locally and it's working.

Lastly, just looking through previous issues and it seems the first p…