fix(ml): race condition when loading models (#3207)

* sync model loading, disabled model ttl by default

* disable revalidation if model unloading disabled

* moved lock

machine-learning/app/main.py

@@ -25,7 +25,7 @@ app = FastAPI()
 
 
 def init_state() -> None:
-    app.state.model_cache = ModelCache(ttl=settings.model_ttl, revalidate=True)
+    app.state.model_cache = ModelCache(ttl=settings.model_ttl, revalidate=settings.model_ttl > 0)
 
 
 async def load_models() -> None: