`Community.decode_map` and associated functions are typed wrong

[qstokkink]

Currently, the Community.decode_map is typed as follows:

self.decode_map: list[Callable[[Community, Address, bytes], None] |
                      Callable[[Address, bytes], None] |
                      None]

This typing is mirrored in other functions like Community.add_message_handler().

The problem is that the typing only allows for callbacks of the following form:

def callback_type1(Community, Address, bytes) -> None: ...
def callback_type2(Address, bytes) -> None: ...
None  # Undefined

However, the following two types are (/should be) also valid:

async def callback_type3(Community, Address, bytes) -> None: ...
async def callback_type4(Address, bytes) -> None: ...