Lifespan context (#361)

**Related Issue(s):**

- #

**Description:**
- Migrated startup event handling from deprecated `@app.on_event("startup")` to FastAPI's recommended lifespan context manager. This removes deprecation warnings and ensures compatibility with future FastAPI versions

**PR Checklist:**

- [x] Code is formatted and linted (run `pre-commit run --all-files`)
- [x] Tests pass (run `make test`)
- [x] Documentation has been updated to reflect changes, if applicable
- [x] Changes are added to the changelog

Author: jonhealy1

stac_fastapi/elasticsearch/stac_fastapi/elasticsearch/app.py

@@ -1,6 +1,9 @@
 """FastAPI application."""
 
 import os
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI
 
 from stac_fastapi.api.app import StacApi
 from stac_fastapi.api.models import create_get_request_model, create_post_request_model
@@ -97,17 +100,21 @@
     search_post_request_model=post_request_model,
     route_dependencies=get_route_dependencies(),
 )
-app = api.app
-app.root_path = os.getenv("STAC_FASTAPI_ROOT_PATH", "")
-
-# Add rate limit
-setup_rate_limit(app, rate_limit=os.getenv("STAC_FASTAPI_RATE_LIMIT"))
 
 
-@app.on_event("startup")
-async def _startup_event() -> None:
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    """Lifespan handler for FastAPI app. Initializes index templates and collections at startup."""
     await create_index_templates()
     await create_collection_index()
+    yield
+
+
+app = api.app
+app.router.lifespan_context = lifespan
+app.root_path = os.getenv("STAC_FASTAPI_ROOT_PATH", "")
+# Add rate limit
+setup_rate_limit(app, rate_limit=os.getenv("STAC_FASTAPI_RATE_LIMIT"))
 
 
 def run() -> None:

stac_fastapi/opensearch/stac_fastapi/opensearch/app.py

@@ -1,6 +1,9 @@
 """FastAPI application."""
 
 import os
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI
 
 from stac_fastapi.api.app import StacApi
 from stac_fastapi.api.models import create_get_request_model, create_post_request_model
@@ -97,18 +100,21 @@
     search_post_request_model=post_request_model,
     route_dependencies=get_route_dependencies(),
 )
-app = api.app
-app.root_path = os.getenv("STAC_FASTAPI_ROOT_PATH", "")
-
-
-# Add rate limit
-setup_rate_limit(app, rate_limit=os.getenv("STAC_FASTAPI_RATE_LIMIT"))
 
 
-@app.on_event("startup")
-async def _startup_event() -> None:
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    """Lifespan handler for FastAPI app. Initializes index templates and collections at startup."""
     await create_index_templates()
     await create_collection_index()
+    yield
+
+
+app = api.app
+app.router.lifespan_context = lifespan
+app.root_path = os.getenv("STAC_FASTAPI_ROOT_PATH", "")
+# Add rate limit
+setup_rate_limit(app, rate_limit=os.getenv("STAC_FASTAPI_RATE_LIMIT"))
 
 
 def run() -> None: