[Gym] Single node tutorial from docs crashes on AttributeError

[jbaczek]

Describe the bug

The example from docs fails on AttributeError:

for metric in self.llm.get_metrics():
                  ^^^^^^^^^^^^^^^^^^^^
AttributeError: 'AsyncLLM' object has no attribute 'get_metrics'

This is caused by the fact that self.llm is an instance of AsyncLLM, not of LLMEngine (which contains get_metrics method). The AsyncLLM is hardcoded and even after removing hardcoded override it fails on some downstream assert telling that I have to use async.

Steps/Code to reproduce bug

Follow steps from the setup guide and the single-node guide.

Expected behavior

The training should not crash!

Additional context

None