[pass] Create check to ensure in-place passes are actually inplace

onnxscript/ir/passes/_pass_infra.py

@@ -136,6 +136,20 @@
                 f"The result of the pass '{self.__class__.__name__}' should be type PassResult. "
                 "Please create one with ir.passes.PassResult()."
             )
+
+        # Checks that the declared in-place property is respected
+        if self.in_place and result.model is not model:
+            raise PassError(
+                f"The pass '{self.__class__.__name__}' is declared in-place, "
+                "but the model returned is *not* the same object as the input model. "
+                "Pass developer: Pass should return the same model object or the in_place property should return False."
+            )
+        if not self.in_place and result.model is model:
+            raise PassError(
+                f"The pass '{self.__class__.__name__}' is declared not in-place, "
+                "but the model returned *is* the same object as the input model. "
+                "Pass developer: Pass should return a new model object or the in_place property should return True."
+            )
         return result
 
     @abc.abstractmethod