Summary

1. If StreamDatasetStorage has only one subset, it's StreamSubset should not calculate length itself and should instead use StreamDatasetStorage length
2. If StreamDatasetStorage has no transformations, it can use its source length

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.
• I have updated the license header for each file (see an example below).

# Copyright (C) 2025 CVAT.ai Corporation
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# SPDX-License-Identifier: MIT