Optimize mapping equality checks and add reverse comparison tests

Agent-Logs-Url: https://github.com/GalacticDynamics/xmmutablemap/sessions/f39253f1-d8ea-46eb-8a8e-f004866a473d

Co-authored-by: nstarman <8949649+nstarman@users.noreply.github.com>

Author: Copilot

src/xmmutablemap/_core.py

@@ -94,7 +94,12 @@ def __eq__(self, other: object) -> bool:
         if isinstance(other, ImmutableMap):
             return self._data == other._data
         if isinstance(other, Mapping):
-            return self._data == dict(other.items())
+            if len(self._data) != len(other):
+                return False
+            sentinel = object()
+            return all(
+                self._data.get(key, sentinel) == value for key, value in other.items()
+            )
         return NotImplemented
 
     # ===========================================

tests/test_immutablemap.py

@@ -67,9 +67,16 @@ def test_hash(self, d: ImmutableMap[str, Any]) -> None:
     def test_eq_with_other_mappings(self) -> None:
         """Test mapping interoperability for `__eq__`."""
         d = ImmutableMap(a=1, b=2)
+        other_dict = {"a": 1, "b": 2}
+        other_ordered_dict = OrderedDict([("a", 1), ("b", 2)])
+        other_proxy = MappingProxyType({"a": 1, "b": 2})
+
         assert d == {"a": 1, "b": 2}
         assert d == OrderedDict([("a", 1), ("b", 2)])
         assert d == MappingProxyType({"a": 1, "b": 2})
+        assert other_dict == d
+        assert other_ordered_dict == d
+        assert other_proxy == d
 
     def test_eq_and_hash_ignore_insertion_order(self) -> None:
         """Test equality/hash contract for same items in different orders."""