[Experimental] Add multi-LoRA support (#1804)

Co-authored-by: Chen Shen <scv119@gmail.com>
Co-authored-by: Shreyas Krishnaswamy <shrekris@anyscale.com>
Co-authored-by: Avnish Narayan <avnish@anyscale.com>

tests/async_engine/test_async_llm_engine.py

@@ -25,6 +25,13 @@ class MockEngine:
         return [RequestOutput(
             request_id=self.request_id)] if self.request_id else []
 
+    async def encode_request_async(
+        self,
+        *args,
+        **kwargs,
+    ):
+        return [1]
+
     def generate(self, request_id):
         self.request_id = request_id
 
@@ -35,6 +42,10 @@ class MockEngine:
         del kwargs  # Unused
         self.add_request_calls += 1
 
+    async def add_request_async(self, **kwargs):
+        del kwargs  # Unused
+        self.add_request_calls += 1
+
     def abort_request(self, request_id):
         del request_id  # Unused
         self.abort_request_calls += 1