There's two udp calls in `UdpTransport._ping()`:
- socket.sendall(b"PINGPING") -> this will be instanteous, AND it will
raise if the receiving side is not listening.
- socket.recv() -> this will wait for SOCKET_TIMEOUT seconds, but only
in case the sendall() succeeded. This means that receiving side exists
and we are now waiting until it's awake enough to respond.
In conclusion, we avoid hammering emulator with PINGPINGs with a timeout
so short we don't see an answer. This should avoid the problem
occasionally seen in CI and described in #1668
API-compatibility with the original one is retained.
Now that we don't need to keep code parity with core, we could do some
changes that make life easier.
All generated classes are now in one file. This makes github diffs more
readable, at the cost of somewhat complicating inspecting individual
classes; however, that is something we shouldn't be doing anyway.
Enums are now implemented as enum.IntEnum.
The original class-level FIELDS member was restored.
Each field is now defined via protobuf.Field, which is easier to work
with in the codec, AND we're not stuffing defaults and flags into the
same field.
