Code quality improvements: version update, type annotation enhancement, and enum usage simplification (#27581)

Signed-off-by: Bradley <bradley.b.pitt@gmail.com>

vllm/v1/core/sched/scheduler.py

@@ -113,14 +113,12 @@ class Scheduler(SchedulerInterface):
         # req_id -> Request
         self.requests: dict[str, Request] = {}
         # Scheduling policy
-        if self.scheduler_config.policy == "priority":
-            self.policy = SchedulingPolicy.PRIORITY
-        elif self.scheduler_config.policy == "fcfs":
-            self.policy = SchedulingPolicy.FCFS
-        else:
+        try:
+            self.policy = SchedulingPolicy(self.scheduler_config.policy)
+        except ValueError as e:
             raise ValueError(
                 f"Unknown scheduling policy: {self.scheduler_config.policy}"
-            )
+            ) from e
         # Priority queues for requests.
         self.waiting = create_request_queue(self.policy)
         self.running: list[Request] = []