Add a generic functional test for `OptiModule.set_state`.

* Add `test_set_state_results` to verify that resetting a modules' state
  enables running the same computation twice. This should enable detecting
  cases when information is missing from the returned state dict.

* Note that at the moment noise-addition modules are ignored. We could look
  into a way to access and restore RNG states (when CSPRNG is not used).