async algorithm conflict with fused optimizer, can only support flattened inplac...

[todo]

bagua/bagua/torch_api/algorithms/async_model_average.py

Lines 84 to 89 in 8707188

	# TODO: async algorithm conflict with fused optimizer, can only support flattened inplace bucket.
	assert do_flatten, "async does not support `do_flatten=False` at present."
	if self.step_id < self.warmup_steps:
	return super().tensors_to_buckets(tensors, do_flatten)
	all_tensors = []

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This issue was generated by todo based on a TODO comment in 8707188. It's been assigned to @wangraying because they committed the code.