Fix typo in doc and check selector

[hiyuchang]

Description

[Please describe the background, purpose, changes made, and how to test this PR]

Checklist

Please check the following items before code is ready to be reviewed.

• Code has passed all tests
• Docstrings have been added/updated in Google Style
• Documentation has been updated
• Code is ready for review

[gemini-code-assist]

Summary of Changes

Hello @hiyuchang, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request improves the project's documentation accuracy and enhances configuration robustness. It addresses a minor typo in the align_with_verl.md tutorial, ensuring consistency in the selector_type setting across both English and Chinese documentation. Additionally, a new validation step has been introduced to proactively check the validity of task_selector.selector_type configurations, preventing potential runtime issues caused by unsupported selector types.

Highlights

• Documentation Typo Fix: Corrected a typo in both the English and Chinese versions of the align_with_verl.md tutorial, changing selector_type:random to the correct selector_type:shuffle.
• Selector Type Validation: Implemented a new validation check in trinity/common/config.py to ensure that the configured task_selector.selector_type is a supported selector, raising a ValueError if an unrecognized type is provided.

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[gemini-code-assist]

Code Review

This pull request introduces a typo fix in the documentation and adds a validation check for the task selector type in the configuration. The documentation change correctly updates random to shuffle. The new validation logic in trinity/common/config.py is a good addition for robustness, ensuring that only supported selectors are used. However, I've noted a minor performance and style issue with an import statement being placed inside a loop. Moving it outside the loop would be an improvement.