state: print encoding error before object

This prevents a very large object string from pushing an error message from
saving (which is usually something informative like "type Foo does not
implement SaverLoader") off the edge of the line. cl/605534648 already did this
for loading.

PiperOrigin-RevId: 631622344

pkg/state/encode.go

@@ -772,7 +772,7 @@ func (es *encodeState) Save(obj reflect.Value) {
 		}
 	}); err != nil {
 		// Include the object in the error message.
-		Failf("encoding error at object %#v: %w", oes.obj.Interface(), err)
+		Failf("encoding error: %w\nfor object %#v", err, oes.obj.Interface())
 	}
 
 	// Check that we have objects to serialize.