docs: async def inject_request_id(app, handler):
      """aiohttp middleware: ensures each request has a unique request ID.
  
      See: ``inject_request_id``.
      """
  
      async def trace_request(request):
          request['x-request-id'] = \
              request.headers.get('x-request-id') or str(uuid.uuid4())
          return await handler(request)
  
      return trace_request