[Feature] Support return logprob of generated tokens (#2784)

* online chat support logprobs

* check xpu

* check vl_gpu_model_runner

* only cuda support logprob

* get_worker() check platform

---------

Co-authored-by: Jiang-Jia-Jun <163579578+Jiang-Jia-Jun@users.noreply.github.com>

fastdeploy/engine/sampling_params.py

@@ -173,6 +173,13 @@ class SamplingParams:
                 f"temperature must be non-negative, got {self.temperature}.")
         if self.top_p is not None and not 0.0 <= self.top_p <= 1.0:
             raise ValueError(f"top_p must be in [0, 1], got {self.top_p}.")
+        # quietly accept -1 as disabled, but prefer 0
+        if self.top_k < -1:
+            raise ValueError(f"top_k must be 0 (disable), or at least 1, "
+                             f"got {self.top_k}.")
+        if not isinstance(self.top_k, int):
+            raise TypeError(
+                f"top_k must be an integer, got {type(self.top_k).__name__}")
 
         if self.max_tokens is not None and self.max_tokens < 1:
             raise ValueError(
@@ -192,6 +199,9 @@ class SamplingParams:
         if self.logprobs is not None and self.logprobs < 0:
             raise ValueError(
                 f"logprobs must be non-negative, got {self.logprobs}.")
+        if self.logprobs is not None and self.logprobs > 20:
+            raise ValueError(
+                "Invalid value for 'top_logprobs': must be less than or equal to 20.")
 
         if not 0 <= self.seed <= 922337203685477580:
             raise ValueError("seed must be in [0, 922337203685477580], got "