[RL] make sync weights conditional (#4925)

* make sync weights conditional

* Also conditionalise vllm creation

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* guard sync for weight sharing

* Guard self.llm access in VLLMGeneration sync_weights and generate patches for PR #4925

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Daniel Han <danielhanchen@gmail.com>