[Core][Bugfix][Perf] Introduce MQLLMEngine to avoid asyncio OH (#8157)

Co-authored-by: Nick Hill <nickhill@us.ibm.com>
Co-authored-by: rshaw@neuralmagic.com <rshaw@neuralmagic.com>
Co-authored-by: Robert Shaw <114415538+robertgshaw2-neuralmagic@users.noreply.github.com>
Co-authored-by: Simon Mo <simon.mo@hey.com>

tests/entrypoints/openai/test_shutdown.py

@@ -44,5 +44,5 @@ async def test_shutdown_on_engine_failure(tmp_path):
                                                 prompt="Hello, my name is")
 
             # Now the server should shut down
-            return_code = remote_server.proc.wait(timeout=3)
+            return_code = remote_server.proc.wait(timeout=8)
             assert return_code is not None