lazy import datasets

[willccbb]

Description

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Test improvement

Testing

• All existing tests pass when running uv run pytest locally.
• New tests have been added to cover the changes

Checklist

• My code follows the style guidelines of this project as outlined in AGENTS.md
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Additional Notes

---

Note

Shifts datasets imports to be lazy to reduce import-time overhead and optionalize the dependency in most code paths. Also tightens typing and forward references.

• Convert top-level datasets imports to TYPE_CHECKING stubs or local imports within functions/methods (e.g., EnvGroup.__init__, Environment.generate, data_utils.load_example_dataset, eval_utils.make_dataset/quiet_datasets, display_utils.BaseDisplay.start/stop)
• Add from __future__ import annotations broadly and change DatasetBuilder to a TypeAlias string; minor typing cleanups
• Update pyproject.toml to include numpy in dependencies

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