[tensor] Add interface for colo tesnor dp size

[yhna940]

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🚨 Issue number

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📝 What does this PR do?

This pull request updates the get_dp_world_size method of the ColoTensor class to provide the distributed data parallel (DP) world size of the tensor (Similar to get_tp_world_size method).

Changes

1. Added the get_dp_world_size method to the ColoTensor class
2. Updated the code that calls tensor.process_group.dp_world_size() to use the new method

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[FrankLeeeee]

Appreciate your contribution!