Refactor ClientRequest (aio-libs#11012)

CHANGES/11012.breaking.rst

@@ -0,0 +1,9 @@
+Refactored ``ClientRequest`` class. This simplifies a lot of code and improves our type
+checking accuracy. It also better aligns public/private attributes with what we expect
+developers to access safely from a client middleware.
+
+If code subclasses ``ClientRequest``, it is likely that the subclass will need tweaking
+to be compatible with the new version. Similarly, subclasses of ``ClientResponse`` may
+need to adjust ``__init__`` parameters.
+
+-- by :user:`Dreamsorcerer`.

aiohttp/client.py

@@ -684,7 +684,7 @@ async def _connect_and_send_request(
                             max_field_size=max_field_size,
                         )
                         try:
-                            resp = await req.send(conn)
+                            resp = await req._send(conn)
                             try:
                                 await resp.start(conn)
                             except BaseException: