[lmi-dist]validate usage lora and speculative together (#1684)

engines/python/setup/djl_python/properties_manager/lmi_dist_rb_properties.py

@@ -56,3 +56,11 @@ def validate_engine(cls, engine):
             raise AssertionError(
                 f"Need MPI engine to start lmi-dist RollingBatcher")
         return engine
+
+    @root_validator(skip_on_failure=True)
+    def validate_speculative_and_lora(cls, properties):
+        if properties["enable_lora"] and properties["speculative_draft_model"]:
+            raise AssertionError(
+                f"Cannot enable lora and speculative decoding at the same time"
+            )
+        return properties