tests(annotations): guard on the 'dataset' extra so base fast-test tier skips cleanly

Fast Pytest Tests failed at COLLECTION in the base '--extra test' tier
with 'ModuleNotFoundError: No module named datasets': tests/annotations/
conftest.py imported the fixture dataset builder (-> lerobot.datasets ->
the HF 'datasets' lib + pandas/pyarrow), which only ship under the
'dataset' extra, so the whole annotations package crashed.

Fix uses the repo's proven module-level guard pattern (see
tests/datasets/test_language.py), NOT a conftest-level importorskip —
verified empirically that pytest.importorskip raised during conftest
*import* is treated as a collection ERROR (exit 1), while module-level
importorskip is a clean SKIP.

  * conftest.py: import build_annotation_dataset LAZILY inside the
    fixtures so the conftest itself imports cleanly in every tier.
  * test_modules / test_validator / test_writer / test_pipeline_recipe_
    render: add module-level pytest.importorskip('datasets') +
    ('pandas') before the pyarrow / lerobot.* imports (# noqa: E402 to
    match the existing convention). pyarrow-importing modules place the
    guard before the pyarrow import.
  * tests/scripts/test_lerobot_annotate.py: same guard (its _push_to_hub
    path imports lerobot.datasets).

Result:
  - base / hardware / viz tiers (no dataset extra): annotation tests
    skip cleanly; the rest of the suite runs -> exit 0.
  - dataset tier: datasets present -> guards pass through -> annotation
    tests run with the stub VLM. The pipeline modules import only
    stdlib + relative + lerobot.datasets (no module-level datatrove /
    vllm / openai), so they import fine there.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/annotations/conftest.py

@@ -26,12 +26,20 @@ from pathlib import Path
 
 import pytest
 
-from tests.fixtures.dataset_factories import build_annotation_dataset
+# NOTE: ``build_annotation_dataset`` pulls in ``lerobot.datasets`` (-> the HF
+# ``datasets`` library + ``pandas``), which only ship under the ``dataset``
+# extra. It is imported LAZILY inside the fixtures below so this conftest
+# imports cleanly in dependency tiers without that extra (e.g. the base
+# ``--extra test`` fast-test tier). The annotation test modules guard
+# themselves with a module-level ``pytest.importorskip("datasets")`` so
+# their collection is skipped — never erroring — when the extra is absent.
 
 
 @pytest.fixture
 def fixture_dataset_root(tmp_path: Path) -> Path:
     """A tiny dataset with two episodes, 12 frames each at 10 fps."""
+    from tests.fixtures.dataset_factories import build_annotation_dataset
+
     return build_annotation_dataset(
         tmp_path / "ds",
         episode_specs=[
@@ -44,6 +52,8 @@ def fixture_dataset_root(tmp_path: Path) -> Path:
 
 @pytest.fixture
 def single_episode_root(tmp_path: Path) -> Path:
+    from tests.fixtures.dataset_factories import build_annotation_dataset
+
     return build_annotation_dataset(
         tmp_path / "ds_one",
         episode_specs=[(0, 30, "Pour water from the bottle into the cup.")],