Summary

To access items from a subset, StreamDataset needs to iterate all the items of the dataset.
It adds a significant overhead if there are a lot of subsets.

Making it more efficient for some cases when the extractor provides access to subsets.

1. if the dataset is not transformed -> no extra iterations
2. if dataset is transformed with local transformations (ItemTransform) and they do not change subsets of items -> one extra iteration to determine whether the condition applies

How to test

Checklist

• I have added unit tests to cover my changes.​
• I have added integration tests to cover my changes.​
• I have added the description of my changes into CHANGELOG.​
• I have updated the documentation accordingly

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
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# Copyright (C) 2025 CVAT.ai Corporation
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# SPDX-License-Identifier: MIT