refactor: use new fastapi lifespan instead of startup/shutdown events (#2294)

* refactor: use new fastapi lifespan instead of events
recommended use: https://fastapi.tiangolo.com/advanced/events/?h=lifespan
threw warnings in pytest
* make startup and shutdown functions
* nix: add override for asgi-lifespan

---------

Co-authored-by: Pavol Rusnak <pavol@rusnak.io>

flake.nix

@@ -33,6 +33,10 @@
             protobuf = prev.protobuf.override { preferWheel = true; };
             ruff = prev.ruff.override { preferWheel = true; };
             wallycore = prev.wallycore.override { preferWheel = true; };
+            # remove the following override when https://github.com/nix-community/poetry2nix/pull/1563 is merged
+            asgi-lifespan = prev.asgi-lifespan.overridePythonAttrs (
+              old: { buildInputs = (old.buildInputs or []) ++ [ prev.setuptools ]; }
+            );
           });
         };
       });