typing support for HCI commands return parameters

[barbibulle]

Add support for proper typing of HCI commands return parameters.
HCI commands are split into two subtypes: synchronous commands, which expect a "command complete" event with a
status a return parameters, and asynchronous commands, which expect a "command status" event with a status, but not return parameters (automatica handling of async command completion will be done in a separate PR, for how they remain
manually-coded).
Synchronous command subclasses have an associated return_parameters_class class, which gets instantiated when the "command complete" event is received.
Sending of commands can still be done with the legacy send_command method, but it is now preferred to use send_sync_command and send_async_commands to get proper typing support.