Move more packet formatting code to dataio

[lmoureaux]

This builds on #2845 to move basic packet serialization logic out of generate_packets.py. Enums and arrays no longer need explicitly generated code; they rely on template functions in dataio instead. For instance, reading a packet now looks like this regardless of the data types involved:

  ...
  /* field 5 is folded into the header */
  /* field 6 is folded into the header */
  if (BV_ISSET(fields, 7)) {
    log_packet_detailed("  field 'name' has changed");
    dio_put(dout, packet->name);
  }
  if (BV_ISSET(fields, 8)) {
    log_packet_detailed("  field 'hp' has changed");
    dio_put(dout, packet->hp, std::uint8_t{});
  }
  if (BV_ISSET(fields, 9)) {
    log_packet_detailed("  field 'activity' has changed");
    dio_put(dout, packet->activity, std::uint8_t{});
  }
  ...

The generated code used to contain a lot of logic such as loops. This is now entirely gone (as far as the dio_* part is concerned).

[jwrober]

Looks like Codacy found some issues. I'd prefer to merge the referenced PR and then rebase this before I review this PR.

[lmoureaux]

Agreed on the rebase. I fixed the unreachable code from codacy, the other checks trigger whenever one uses memcpy() (also when it is used correctly).