alltoallv communication operator support

[cyx-6]

📌 Description

Introduce alltoallv communication operators.

🔍 Related Issues

🚀 Pull Request Checklist

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✅ Pre-commit Checks

• I have installed pre-commit by running pip install pre-commit (or used your preferred method).
• I have installed the hooks with pre-commit install.
• I have run the hooks manually with pre-commit run --all-files and fixed any reported issues.

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🧪 Tests

• Tests have been added or updated as needed.
• All tests are passing (unittest, etc.).

Reviewer Notes

[cyx-6]

above issues are all fixed

[cyx-6]

removed and decoupled

[yongwww]

The multi-gpu tests are skipped in CI due to the ci resource limit. They pass on my multi-B200 node.