test: make test_stream_run.py resolve its feature group standalone

[dchaudhari7177]

Closes #1084.

The dependency

test_stream_run.py requests the feature EngineRunnerTest1. Its FeatureGroup is defined in tests/test_core/test_integration/test_core/test_runner_one_compute_framework.py. Resolution walks live FeatureGroup subclasses, so that module has to be imported before stream_run plans.

Nothing in test_stream_run.py imported it. The tests passed only because tests/test_core/test_runtime/conftest.py imports that module for test_stream_all.py, and a full run collects the sibling package first.

Reproduction, on a clean tree

pytest tests/test_core/test_api/test_stream_run.py -q

FAILED TestStreamRunReturnsGenerator::test_stream_run_returns_generator_type
FAILED TestStreamRunReturnsGenerator::test_stream_run_is_not_a_list
mloda.core.prepare.identify_feature_group.FeatureResolutionError:
No feature groups found for feature name: 'EngineRunnerTest1'.

2 failed, 1 passed. A full tox run is green, which is what kept this invisible at the gate.

The change

Import the defining module from the test module itself — the same one-line registration tests/test_core/test_runtime/conftest.py already relies on, with the same reasoning in a comment.

tests/test_core/test_runtime/conftest.py is left in place: test_stream_all.py still needs it, and it is that package's own registration.

Verification

command	before	after
pytest tests/test_core/test_api/test_stream_run.py	2 failed, 1 passed	3 passed
pytest .../test_stream_run.py .../test_runtime/test_stream_all.py	8 passed	8 passed

Gates on the changed file: ruff format --check --line-length 120, ruff check, mypy --strict --ignore-missing-imports all clean.

One unrelated line in the same file

The module docstring still claimed:

All tests are expected to FAIL because:

• mlodaAPI does not have a stream_run method yet

stream_run exists and the file has been green in full runs for a while, so that paragraph is dropped. Happy to pull it back out if you would rather keep this diff to the import alone.