📝 Update source examples and docs from Python 3.9 to 3.10 (#14900)

docs_src/middleware/tutorial001_py310.py

@@ -0,0 +1,14 @@
+import time
+
+from fastapi import FastAPI, Request
+
+app = FastAPI()
+
+
+@app.middleware("http")
+async def add_process_time_header(request: Request, call_next):
+    start_time = time.perf_counter()
+    response = await call_next(request)
+    process_time = time.perf_counter() - start_time
+    response.headers["X-Process-Time"] = str(process_time)
+    return response