Every message sent through send_message or the entity paths needed a
proto_encode_msg<T> thunk (17 bytes on xtensa) and, for entity state
and info messages, a calc_size<T> thunk, because the generated encode
and calculate_size were member functions and the connection code wants
plain function pointers over const void *.
The generator now emits the bodies as static encode_msg(const void *)
and calc_size_msg(const void *) functions, so &T::encode_msg is
already a MessageEncodeFn and the thunks disappear. The member
encode() and calculate_size() remain as inline forwarders for direct
callers. ProtoMessage carries the same static defaults for messages
without fields, which also removes the separate no-op encode thunk.
A call that drops the returned cursor would silently truncate the message, so the
compiler now warns on it and a unit test scans the generated file for the same mistake.
Also corrects the outlining comment for ESP8266, where the inline write is a few byte
stores rather than one, and the RAW_ENCODE_MAP annotation.
J. Nick Koston