Optimise the _ensure_not_equal function

Co-authored-by: Ricardo Vieira <[email protected]>

Author: Abhinav-Khot

pytensor/tensor/einsum.py

@@ -421,10 +421,12 @@ def _ensure_not_equal(elements):
     """
     Ensures that any pair in a list of elements are not the same object. If a pair of elements is found to be equal, then one of them is converted to a copy.
     """
-    for i in range(len(elements)):
-        for j in range(i + 1, len(elements)):
-            if elements[i] == elements[j]:
-                elements[j] = elements[j].copy()
+    elements = list(elements)
+    n_elem = len(elements)
+    for i, elem1 in enumerate(elements[:-1]):
+        for j, elem2 in enumerate(elements[i + 1:], start=i+1):
+            if elem1 is elem2:
+                elements[j] = elem1.copy()
     return elements