[tensor] refactor colo-tensor (#992)

* refactor colo-tensor and update linear op

* polish code

* polish code

* update ops and unit tests

* update unit tests

* polish code

* rename dist_spec module

* polish code

* polish code

* remove unneeded import

* fix pipelinable

colossalai/tensor/_ops/_utils.py

@@ -0,0 +1,12 @@
+import torch
+from typing import Union, Optional
+from colossalai.tensor import ColoTensor
+
+GeneralTensor = Union[ColoTensor, torch.Tensor]
+Number = Union[int, float]
+
+
+def convert_to_colo_tensor(tensor: Optional[GeneralTensor]) -> Optional[ColoTensor]:
+    if tensor is not None and not isinstance(tensor, ColoTensor):
+        tensor = ColoTensor.from_torch_tensor(tensor)
+    return tensor