py/objarray: Prohibit comparison of mismatching types.

Array equality is defined as each element being equal but to keep
code size down MicroPython implements a binary comparison.  This
can only be used correctly for elements with the same binary layout
though so turn it into an NotImplementedError when comparing types
for which the binary comparison yielded incorrect results: types
with different sizes, and floating point numbers because nan != nan.

tests/basics/array_micropython.py

@@ -17,3 +17,15 @@ print(a[0])
 a = array.array('P')
 a.append(1)
 print(a[0])
+
+# comparison between mismatching binary layouts is not implemented
+typecodes = ["b", "h", "i", "l", "q", "P", "O", "S", "f", "d"]
+for a in typecodes:
+    for b in typecodes:
+        if a == b and a not in ["f", "d"]:
+            continue
+        try:
+            array.array(a) == array.array(b)
+            print('FAIL')
+        except NotImplementedError:
+            pass