Connection returned to pool in inconsistent state when `asyncio.CancelledError` occurs

I encountered an issue in the `acquire` decorator where a connection may be returned to the pool in an inconsistent state.

This happens because `asyncio.CancelledError` inherits from `BaseException`, not from `Exception`. As a result, it is not caught by the `except Exception` block.

Relevant code:
[https://github.com/aio-libs/aiomcache/blob/master/aiomcache/client.py#L28](https://github.com/aio-libs/aiomcache/blob/master/aiomcache/client.py#L28)

Because of this, when a coroutine is cancelled, `conn[0].set_exception(exc)` is not called before `self._pool.release(conn)`.

As a result, a broken connection can be returned to the pool and reused later, which may lead to errors like:

```
ValueError: Separator is not found, and chunk exceed the limit
```

This can be fixed by explicitly handling `asyncio.CancelledError` and marking the connection as failed before returning it to the pool.

Example:

```python
def acquire(
func: Callable[Concatenate[_Client, Connection, _P], Awaitable[_T]]
) -> Callable[Concatenate[_Client, _P], Awaitable[_T]]:

@functools.wraps(func)
async def wrapper(self: _Client, *args: _P.args, # type: ignore[misc]
**kwargs: _P.kwargs) -> _T:
conn = await self._pool.acquire()
try:
return await func(self, conn, *args, **kwargs)
except Exception as exc:
conn[0].set_exception(exc)
raise
except asyncio.CancelledError as exc:
# Got CancelledError from client code.
conn[0].set_exception(exc)
raise
finally:
self._pool.release(conn)

return wrapper
```