[Sampler] Support returning all logprobs or logits (#21792)

Signed-off-by: 22quinn <33176974+22quinn@users.noreply.github.com>

vllm/v1/engine/logprobs.py

@@ -138,7 +138,7 @@ class LogprobsProcessor:
 
     def pop_prompt_logprobs(self) -> Optional[PromptLogprobs]:
         """Pop and return all request prompt logprobs
-        
+
         The logprobs processor aggregates prompt chunk logprobs
         over one or more prefill chunks. This method returns
         all prompt logprobs at once and then forgets them.
@@ -176,7 +176,8 @@ class LogprobsProcessor:
         Returns:
           dict[token id, Logprob]
         """
-
+        if num_logprobs == -1:
+            num_logprobs = len(logprobs)
         # We do not need a special case for the sampled token
         # being in the topk, since inserting duplicated data
         # into a dictionary twice is the same as doing it once.