[Speculative decoding] Adding configuration object for speculative decoding (#3706)

Co-authored-by: Lily Liu <lilyliupku@gmail.com>

vllm/executor/ray_gpu_executor.py

@@ -6,7 +6,8 @@ from collections import defaultdict
 from typing import TYPE_CHECKING, Any, Dict, List, Optional
 
 from vllm.config import (CacheConfig, DeviceConfig, LoRAConfig, ModelConfig,
-                         ParallelConfig, SchedulerConfig, VisionLanguageConfig)
+                         ParallelConfig, SchedulerConfig, SpeculativeConfig,
+                         VisionLanguageConfig)
 from vllm.engine.ray_utils import RayWorkerVllm, ray
 from vllm.executor.executor_base import ExecutorAsyncBase, ExecutorBase
 from vllm.executor.utils import check_block_size_valid
@@ -41,6 +42,7 @@ class RayGPUExecutor(ExecutorBase):
         device_config: DeviceConfig,
         lora_config: Optional[LoRAConfig],
         vision_language_config: Optional[VisionLanguageConfig],
+        speculative_config: Optional[SpeculativeConfig],
     ) -> None:
         self.model_config = model_config
         self.cache_config = cache_config
@@ -49,6 +51,8 @@ class RayGPUExecutor(ExecutorBase):
         self.scheduler_config = scheduler_config
         self.device_config = device_config
         self.vision_language_config = vision_language_config
+        assert (not speculative_config
+                ), "Speculative decoding not yet supported for RayGPU backend."
 
         assert self.parallel_config.worker_use_ray
         placement_group = self.parallel_config.placement_group