Refactor to protobuf

[tolauwae]

Refactors the existing debugger API using a protobuf scheme. The new scheme his optimized for low message size.

protobuf scheme

Protobuf defines two message type enums:

• Command: Frontend -> WARDuino
• Notification: WARDuino -> frontend

For instance:

enum Command {
  COMMAND_RUN = 0;                 // no payload
  COMMAND_HALT = 1;                // no payload
  //...
}

Payloads are defined in protobuf as messages. For instance:

message CodeLocation {
    uint32 module_index = 1;
    uint32 program_counter = 2;
}

message Breakpoint {
    CodeLocation location = 1;
}

Debug messages are not fully encoded by protobuf, only these payload.
This means that debug messages are of this form:

[type: uint8][payload length: varint][protobuf payload]

This allows for minimal message size. Sending messages looks like this:

write_byte(COMMAND_CONTINUE_FOR);
write_length(payload_size);
pb_encode(&stream, ContinueFor_fields, &message);

Which results in this message on the wire:

┌────────────┬────────────┬───────────────────────────────┐
│ type       │ length     │ encoded ContinueFor (payload) │
│ 22         │ 2          │ 08 05                         │
└────────────┴────────────┴───────────────────────────────┘

ABI improvements

Improvements are split over the entire PR stack. (#406, #411, #413)

• adapted for multiple modules (vm support since Support for multiple modules #338): all code locations are now module index + pc counter
• DUMP commands and inspect have been removed over the more general snapshot
• function updates now only change function bodies, type signatures stay the same

[MaartenS11]

Oh wow the Zephyr binary size is actually slightly smaller than the current size on main.

[MaartenS11]

Makes me wonder, should we still even have dump since it's the same as snapshot? Command dump and command snapshot are just the same at this point, might be good to just remove one now.

[tolauwae]

agreed, will remove

[MaartenS11]

Support for full seems to have gone missing here (just putting that here so we don't forget).

[MaartenS11]

Would be nice to have some comments/documentation of how this works.

[tolauwae]

this code has been removed

[MaartenS11]

Seems a bit strange to have functionBodies as a field in the Debugger but maybe it's used somewhere else that I'm not aware of.