Compared decoder.js against the MeshCore firmware source (Dispatcher.cpp,
Packet.h, Mesh.cpp, AdvertDataHelpers.h) and fixed all mismatches:
1. Field order: transport codes now parsed BEFORE path_length byte,
matching the spec: [header][transport_codes?][path_length][path][payload]
2. ACK payload: was incorrectly decoded as dest(1)+src(1)+ackHash(4).
Firmware shows ACK is just checksum(4) — no dest/src hashes.
3. TRACE payload: was incorrectly decoded as flags(1)+tag(4)+dest(6)+src(1).
Firmware shows tag(4)+authCode(4)+flags(1)+pathData.
4. ADVERT appdata: added missing feature1 (0x20 flag) and feature2
(0x40 flag) parsing — 2-byte fields between location and name.
5. Transport code field naming: renamed nextHop/lastHop to code1/code2
to match spec terminology (transport_code_1/transport_code_2).
6. Fixed incorrect field size labels in packets.js hex breakdown:
dest/src are 1 byte, MAC is 2 bytes (not 6B/6B/4B).
7. Fixed ANON_REQ/PATH comment typos (dest was listed as 6 bytes,
MAC as 4 bytes — both wrong, code was already correct).
All 329 tests pass (66 decoder + 263 spec/golden).
