[FEA]: Add tensor_count property for ControlMessage

[yczhang-nv]

Is this a new feature, an improvement, or a change to existing functionality?

Improvement

How would you describe the priority of this feature request

Low (would be nice)

Please provide a clear description of problem this feature solves

For ControlMessage, msg.tensors().count is a common pattern, calling msg.tensors() might require a bit more cost than we think, we might want to consider a tensor_count property.

See #1803 (comment)

Describe your ideal solution

Add a tensor_count property for ControlMessage.

Additional context

No response

Code of Conduct

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• I have searched the open feature requests and have found no duplicates for this feature request