test(tirx): document why test_eq_ops keeps == None / != None

The `== None` / `!= None` comparisons in `test_eq_ops` are intentional:
the test exercises the overloaded `__eq__` / `__ne__` operators on
`IntImm` / `StringImm`, which raise `ValueError` when coerced to bool.
Rewriting them as `is None` / `is not None` bypasses the overloads and
breaks the test, so add a NOTE comment flagging the constraint.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: MasterJH5574

tests/python/tirx-base/test_tir_base.py

@@ -176,6 +176,10 @@ def test_exception():
 
 
 def test_eq_ops():
+    # NOTE: the `== None` / `!= None` below are intentional and must NOT be
+    # rewritten as `is None` / `is not None`. This test exercises the overloaded
+    # `__eq__` / `__ne__` operators on `IntImm` / `StringImm`; the `is` operators
+    # bypass those overloads and would defeat the test.
     a = tirx.IntImm("int8", 1)
     with pytest.raises(ValueError):
         assert a != None