[zero] Suggests a minor change to confusing variable names in the ZeRO optimizer. (#3173)

* Fix confusing variable name in zero opt

* Apply lint

* Fix util func

* Fix minor util func

* Fix zero param optimizer name

colossalai/zero/low_level/_utils.py

@@ -91,10 +91,18 @@ def get_grad_accumulate_object(tensor):
     return grad_acc_obj
 
 
-def split_half_float_double(tensor_list):
+def split_by_dtype(tensor_list):
+    """
+    Splits a list of PyTorch tensors into sublists based on their data type.
+
+    :param tensor_list: A list of PyTorch tensors.
+    :type tensor_list: list[torch.Tensor]
+    :return: A list of sublists, where each sublist contains tensors of a specific data type.
+    :rtype: list[list[torch.Tensor]]
+    """
     dtypes = ["torch.cuda.HalfTensor", "torch.cuda.FloatTensor", "torch.cuda.DoubleTensor", "torch.cuda.BFloat16Tensor"]
     buckets = []
-    for i, dtype in enumerate(dtypes):
+    for _, dtype in enumerate(dtypes):
         bucket = [t for t in tensor_list if t.type() == dtype]
         if bucket:
             buckets.append(bucket)