Add a TF1-compatible version of SavedModelPolicy.
Add a TF1-compatible version of SavedModelPolicy.

Currently with TF2 disabled, running locally on CPU, I only get about 16 steps-per-second from the existing SavedModelPolicy. With this change it increases up to around 450 SPS, in line with what I get when TF2 is enabled.

PiperOrigin-RevId: 450042131
Change-Id: Ibffb79ed862d874e038b8e74daea9982dbe9beba

deepmind/meltingpot,deepmind/meltingpot