- Fixed FSDP1 model offload
- With `actor_rollout_ref.actor.fsdp_config.param_offload=True \` and
`actor_rollout_ref.actor.fsdp_config.optimizer_offload=True \ `. The GPU
memory utilization can increase to 0.9
- With actor, critic and reference offload all enabled, there will only
be one model copy at a time in the GPU memory. Therefore, we can further
increase the `micro_batch_size_per_gpu` or `max_token_per_gpu`

**Specifically:**
- During rollout, only rollout model and KVCache are in the GPU memory.
- During critic compute values, only the critic model will stay in the
GPU memory while its optimizer and other model states are in CPU main
memory
- During actor update, the actor model, optimizer are stored on GPU
while the reference model and critic model, critic optimizer are
offloaded to CPU.