[AsyncScheduling] Make async overlap work with logprobs (#27615)

Signed-off-by: Nick Hill <nhill@redhat.com>

tests/conftest.py

@@ -831,8 +831,9 @@ class VllmRunner:
         images: PromptImageInput | None = None,
         videos: PromptVideoInput | None = None,
         audios: PromptAudioInput | None = None,
+        return_logprobs: bool = False,
         **kwargs: Any,
-    ) -> list[tuple[list[list[int]], list[str]]]:
+    ) -> list[tuple[list[list[int]], list[str]]] | tuple[list, list]:
         inputs = self.get_inputs(prompts, images=images, videos=videos, audios=audios)
 
         req_outputs = self.llm.generate(
@@ -840,18 +841,23 @@ class VllmRunner:
         )
 
         outputs: list[tuple[list[list[int]], list[str]]] = []
+        logprobs = []
         for req_output in req_outputs:
             prompt_str = req_output.prompt
             prompt_ids = req_output.prompt_token_ids
             req_sample_output_ids: list[list[int]] = []
             req_sample_output_strs: list[str] = []
+            req_logprobs = []
             for sample in req_output.outputs:
                 output_str = sample.text
                 output_ids = list(sample.token_ids)
                 req_sample_output_ids.append(prompt_ids + output_ids)
                 req_sample_output_strs.append((prompt_str or "") + output_str)
+                if sample.logprobs:
+                    req_logprobs.extend(sample.logprobs)
             outputs.append((req_sample_output_ids, req_sample_output_strs))
-        return outputs
+            logprobs.append(req_logprobs)
+        return outputs if not return_logprobs else (outputs, logprobs)
 
     @staticmethod
     def _final_steps_generate_w_logprobs(