Breaking changes and deprecations since v0.5

[eric-haibin-lin]

rollout

• chat completion api will be removed: [rollout] feat: remove chat scheduler #2725. Use token-in-token-out agent loop instead https://github.com/volcengine/verl/tree/main/verl/experimental/agent_loop
• actor_rollout_ref.rollout.name default value is removed and must be specified by the user [BREAKING] [rollout] chore: remove default rollout selection #2757
• tool creation API is updated for more general usage [tool, sglang] feat: add tool create info #2870

[frrad]

#2701 will deprecate compute_policy_loss in favor of compute_policy_loss_vanilla