OM_DVGEOCOMP tests and forward mode derivatives

pygeo/mphys/mphys_dvgeo.py

@@ -947,3 +947,5 @@
                                     # in multiple objective seeds with totalSensitivity. we can remove the [0]
                                     # once we move back to totalSensitivityTransProd
                                     d_inputs[k] += xdotg[k][0]
+        elif mode != "rev":
+            raise RuntimeError(f'OM_DVGEOCOMP supports only "rev" derivative mode, but "{mode}" was selected')