gh-142044: Add note to prefer asyncio.timeout/timeout_at over Timeout

Document that users should prefer using asyncio.timeout() or
asyncio.timeout_at() rather than directly instantiating the Timeout
class, matching the guidance already present in the source code.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kovan

Doc/library/asyncio-task.rst

@@ -771,6 +771,11 @@ Timeouts
        An :ref:`asynchronous context manager <async-context-managers>`
        for cancelling overdue coroutines.
 
+       .. note::
+
+          Prefer using :func:`asyncio.timeout` or :func:`asyncio.timeout_at`
+          rather than instantiating :class:`Timeout` directly.
+
        ``when`` should be an absolute time at which the context should time out,
        as measured by the event loop's clock: