feat(utils): add 'label_folder_name' to 'img2label_paths' function

[songsnim]

1. Check for Existing Contributions ✅ I have checked existing PRs and this contribution is unique.

2. Link Related Issues N/A. This PR is a proactive improvement to enhance function reusability and does not address a specific open issue.

3. Purpose of Change

• The existing img2label_paths function was not flexible because the label folder name was hardcoded as 'labels'. This made it difficult to reuse the function for datasets with different directory structures (e.g., annotations, yolo_txts).
• This change is very useful when you experiment with training a single set of images against several different sets of labels. (labels_with_A_scheme, labels_with_B_scheme, etc...)

4. Description of Change

• Added a new parameter, label_folder_name, to the img2label_paths function.
• Specifying label_folder_name in the .yaml file sets the training label directory to be that folder, located alongside the images directory
• Set the default value to 'labels' to ensure backward compatibility, meaning existing code that uses this function will not break.

Modified the path string generation to use this new parameter dynamically.

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Adds flexibility to map image paths to label paths by allowing custom label folder names instead of only "labels". 🗂️✨

📊 Key Changes

• Updated img2label_paths to:
  • Accept any iterable of image paths (type hint relaxed).
  • Support a configurable label folder name via a new parameter label_folder_name (default: "labels").
  • Preserve existing behavior while enabling alternative directory structures.

🎯 Purpose & Impact

• Enables datasets that use non-standard label folder names (e.g., "ann", "annotations") without extra preprocessing. 🔧
• Improves compatibility with diverse dataset layouts, making data integration smoother. 🤝
• Maintains backward compatibility for existing users and pipelines. ✅

[github-actions[bot]]

All Contributors have signed the CLA. ✅
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Notes on your PR:

• Nice enhancement to img2label_paths with the new label_folder_name parameter while keeping default behavior for backward compatibility. 🙌
• If this feature affects dataset YAML usage or examples, please consider adding a brief note or example in the docs and tests to validate alternate label directory names. 🧪📚

If your PR addresses a bug, please also include a Minimum Reproducible Example (MRE) detailing:

1. The exact steps or code snippet to reproduce
2. Expected vs. actual behavior
3. Environment details (OS, Python, package versions) This helps us verify and merge your fix faster. 🙏

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Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests.

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[songsnim]

I have read the CLA Document and I sign the CLA

[roel-klein]

this would be an useful addition that a lot of people could benefit from, see also pull requests #21430, #20870 and issues #9087, #12986

[glenn-jocher]

Thanks, agreed—this is useful; we’ll review alongside #21430, #20870 and the related issues to consolidate behavior, and pending a small unit test plus threading the YAML key through YOLODataset so img2label_paths actually receives label_folder_name, we’ll move it forward.

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👋 Hello there! We wanted to let you know that we've decided to close this pull request due to inactivity. We appreciate the effort you put into contributing to our project, but unfortunately, not all contributions are suitable or aligned with our product roadmap.

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