Reduce memory use and copies by storing the TrainInputs directly in the replay buffer.
Reduce memory use and copies by storing the TrainInputs directly in the replay buffer.

PiperOrigin-RevId: 304390738
Change-Id: Ic5442fbedb57ba5bcce306ca9d31fcf81b276f8c

deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel,deepmind/open_spiel