Fix
* Avoid double buffering when using asyncio reader without `negotiate_unix_fd` ([213](https://github.com/Bluetooth-Devices/dbus-fast/issues/213)) ([`c933be7`](https://github.com/Bluetooth-Devices/dbus-fast/commit/c933be709508e0504e97254247bec70eb9e8c6d4))
* Additionally, the above change fixes a long standing bug in the `negotiate_unix_fd` path as it did not check for `EAGAIN` or `EWOULDBLOCK` which could result in unexplained failures when the header was sent but the message body was not available on the wire yet ([213](https://github.com/Bluetooth-Devices/dbus-fast/issues/213)) ([`c933be7`](https://github.com/Bluetooth-Devices/dbus-fast/commit/c933be709508e0504e97254247bec70eb9e8c6d4))