fix: torch backend mean reverted to work with keepdim, out args, …

…as well as `dtype` (#28742)

ivy/functional/backends/torch/statistical.py

@@ -97,10 +97,14 @@ def mean(
     if dtype is not None:
         dtype = ivy.as_native_dtype(dtype)
     if axis is None:
-        ret = torch.mean(input=x, dtype=dtype)
-    else:
-        ret = torch.mean(input=x, dim=axis, keepdims=keepdims, dtype=dtype, out=out)
-    return ret
+        num_dims = len(x.shape)
+        axis = list(range(num_dims))
+    if axis in [(), []]:
+        if ivy.exists(out):
+            return ivy.inplace_update(out, x)
+        else:
+            return x
+    return torch.mean(x, dim=axis, dtype=dtype, keepdim=keepdims, out=out)
 
 
 mean.support_native_out = True