Add test for repeated saving/loading and make it work. Also adding one more...

Add test for repeated saving/loading and make it work. Also adding one more test for kwargs and concrete_functions.

Note that cycling (repeated save/restore) does not work for nested functions yet, but I am submitting this test to prevent more damage in the future: every new feature should ensure that cycling works properly with it.

PiperOrigin-RevId: 230516944