[Fix] CommReduce could handle 0-dim data

[flashmouse]

This PR try to fix #19676 , allow CommReduce handle 0-dim data correctly.

[gemini-code-assist]

Code Review

This pull request fixes a crash when reducing a 0-dimensional (scalar) tensor by returning its identity instead of throwing an error, and adds a corresponding regression test. The reviewer pointed out that when ndim == 0 and atleast1d is true, the output tensor should be expanded to at least 1-dimensional (e.g., shape [1]) using topi::expand_dims rather than returning the 0-dimensional identity directly.

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[gemini-code-assist]

When ndim == 0 and atleast1d is true, the output tensor should be at least 1-dimensional (i.e., shape [1]). However, returning topi::identity directly ignores the atleast1d flag and returns a 0-dimensional tensor. We should wrap the identity tensor with topi::expand_dims if atleast1d is enabled.

Suggested change

	if (ndim == 0) {
	return topi::identity(data, data->op->name + "_red", kCommReduce);
	}
	if (ndim == 0) {
	auto identity = topi::identity(data, data->op->name + "_red", kCommReduce);
	return atleast1d ? topi::expand_dims(identity, 0, 1) : identity;
	}