[Speculators][Speculative Decoding] Add Qwen Eagle3 Support (#21835)

Signed-off-by: Dipika Sikka <dipikasikka1@gmail.com>

vllm/model_executor/models/qwen3.py

@@ -288,6 +288,13 @@ class Qwen3ForCausalLM(nn.Module, SupportsLoRA, SupportsPP):
         self.make_empty_intermediate_tensors = (
             self.model.make_empty_intermediate_tensors)
 
+    def set_aux_hidden_state_layers(self, layers: tuple[int]) -> None:
+        self.model.aux_hidden_state_layers = layers
+
+    def get_eagle3_aux_hidden_state_layers(self) -> tuple[int]:
+        num_layers = len(self.model.layers)
+        return (2, num_layers // 2, num_layers - 3)
+
     def get_input_embeddings(self, input_ids: torch.Tensor) -> torch.Tensor:
         return self.model.get_input_embeddings(input_ids)