Add Olmo3 architecture adapter tests

tests/unit/model_bridge/supported_architectures/test_olmo3_adapter.py

@@ -0,0 +1,24 @@
+"""Unit tests for Olmo3ArchitectureAdapter.
+
+The adapter body is `pass` — it inherits its config, component mapping, and
+weight conversions unchanged from Olmo2ArchitectureAdapter (covered by
+test_olmo2_adapter.py). The only contract this subclass owns is the subclass
+relationship itself.
+"""
+
+from transformer_lens.model_bridge.supported_architectures.olmo2 import (
+    Olmo2ArchitectureAdapter,
+)
+from transformer_lens.model_bridge.supported_architectures.olmo3 import (
+    Olmo3ArchitectureAdapter,
+)
+
+
+class TestOlmo3Inheritance:
+    """Subclass relationship to Olmo2ArchitectureAdapter. The class body is
+    `pass`, so the inherited surface is the contract worth pinning. A future
+    accidental override would be caught here.
+    """
+
+    def test_subclass_of_olmo2(self) -> None:
+        assert issubclass(Olmo3ArchitectureAdapter, Olmo2ArchitectureAdapter)