[Misc] fix: add miss best_of param validation (#18555)

Signed-off-by: googs1025 <googs1025@gmail.com>

vllm/sampling_params.py

@@ -389,6 +389,17 @@ class SamplingParams(
                              f"type {type(self.n)}")
         if self.n < 1:
             raise ValueError(f"n must be at least 1, got {self.n}.")
+        if self.best_of is not None:
+            if not isinstance(self.best_of, int):
+                raise ValueError(
+                    f"best_of must be an integer, got {type(self.best_of)}")
+            if self.best_of < 1:
+                raise ValueError(
+                    f"best_of must be at least 1, got {self.best_of}")
+            if self.best_of < self.n:
+                raise ValueError(
+                    f"best_of must be greater than or equal to n, "
+                    f"got n={self.n} and best_of={self.best_of}.")
         if not -2.0 <= self.presence_penalty <= 2.0:
             raise ValueError("presence_penalty must be in [-2, 2], got "
                              f"{self.presence_penalty}.")