Remove deprecated FastAPI events

FastAPI's startup and shutdown events have been deprecated and replaced with a single 'lifespan' context manager.

src/exposurelog/main.py

@@ -1,3 +1,6 @@
+from collections.abc import AsyncIterator
+from contextlib import asynccontextmanager
+
 import fastapi
 import fastapi.responses
 import starlette.requests
@@ -14,7 +17,15 @@
     get_message,
 )
 
-app = fastapi.FastAPI()
+
+@asynccontextmanager
+async def lifespan(app: fastapi.FastAPI) -> AsyncIterator[None]:
+    await shared_state.create_shared_state()
+    yield
+    await shared_state.delete_shared_state()
+
+
+app = fastapi.FastAPI(lifespan=lifespan)
 
 subapp = fastapi.FastAPI(
     title="Exposure log service",
@@ -52,13 +63,3 @@ async def root(request: starlette.requests.Request) -> str:
         but harder to read.
     </html>
     """
-
-
-@app.on_event("startup")
-async def startup_event() -> None:
-    await shared_state.create_shared_state()
-
-
-@app.on_event("shutdown")
-async def shutdown_event() -> None:
-    await shared_state.delete_shared_state()

src/exposurelog/testutils.py

@@ -88,19 +88,14 @@ async def create_test_client(
             **db_config,
         ):
             # Note: httpx.AsyncClient does not trigger startup and shutdown
-            # events. We could use asgi-lifespan's LifespanManager,
-            # but it does not trigger the shutdown event if there is
-            # an exception, so it does not seem worth the bother.
+            # events, so we have to manually trigger the lifespan events.
             assert not shared_state.has_shared_state()
-            await main.startup_event()
-            try:
+            async with main.lifespan(main.app):
                 async with httpx.AsyncClient(
                     app=main.app, base_url="http://test"
                 ) as client:
                     assert shared_state.has_shared_state()
                     yield client, messages
-            finally:
-                await main.shutdown_event()
 
 
 @contextlib.contextmanager