[bluetooth.govee] Enable accessing Govee devices with updated firmware requiring encrypted communication

Newer firmwares for Govee devices encrypt the communication for the
command channel. Every communication on the PROTOCOL_CHAR_UUID
characteristic for these devices is expected to be encrypted and if
that does not hold, the device will immediately disconnect.

The communication is protected by a session key, that is determined by
doing a handshake with the auth service on the device. That in turn is
authenticated with a pre shared key, that other projects communicating
with the devices already determined.

The general communication scheme is:

- connect to device
- do encryption handshake to determine session key
- communicate with PROTOCOL_CHAR_UUID using session key
- disconnect

While working on the implementation the asynchronous implementation
allowing multiple threads access to the device simultaniously was
found to be problematic.

Changes:

- ConnectedBluetoothHandler was dropped as superclass and replaced by
  BeaconBluetoothHandler as the core functionality (reporting the
  current measurements) is provided by the advertisement data and the
  connection is only needed to update the configuration.
- The socket like implementation (gattserial) was removed and replaced
  by direct invocation of BluetoothDevice#writeCharacteristic and
  event listeners for onCharacteristicUpdate. From that infrastructure
  the implemented commands were retained as they provide the required
  encoding.
- A helper to handle the encryption was added. This helper also
  provides a NOOP implementation if the device does not have an auth
  service and thus does not need encryption.

Signed-off-by: Matthias Bläsing <mblaesing@doppel-helix.eu>

Author: matthiasblaesing