remove .item which causes sync issues (Lightning-AI#1254)

* remove .item which causes sync issues

* fixed gradient acc sched

* fixed gradient acc sched

pytorch_lightning/trainer/supporting_classes.py

@@ -0,0 +1,39 @@
+import torch
+
+
+class TensorRunningMean(object):
+    """
+    Tracks a running mean without graph references.
+    Round robbin for the mean
+    """
+    def __init__(self, window_length):
+        self.window_length = window_length
+        self.reset()
+        self.last_idx = 0
+
+    def reset(self):
+        self.memory = torch.Tensor(self.window_length)
+        self.current_idx = 0
+
+    def last(self):
+        return self.memory[self.last_idx]
+
+    def append(self, x):
+        # map proper type for memory if they don't match
+        if self.memory.type() != x.type():
+            self.memory.type_as(x)
+
+        # store without grads
+        with torch.no_grad():
+            self.memory[self.current_idx] = x
+            self.last_idx = self.current_idx
+
+        # increase index
+        self.current_idx += 1
+
+        # reset index when hit limit of tensor
+        if self.current_idx >= self.window_length:
+            self.current_idx = 0
+
+    def mean(self):
+        return self.memory.mean()