Documentation: Would be nice to have some visual diagram about the meshcore packet structure

[mofosyne]

Was looking at https://github.com/ripplebiz/MeshCore/blob/main/src/Packet.h and it's not exactly easy to get a general sense as to what the general structure looks like in the wire.

Would be nice to have an ASCII or svg diagram to illustrate the overall structure at least.

[tbb98]

Packet Structure

Field	Size (bytes)	Description
header	1	Contains routing type, payload type, and payload version.
payload_len	2	Length of the payload in bytes.
path_len	2	Length of the path field in bytes.
path	MAX_PATH_SIZE	Stores the routing path if applicable.
payload	MAX_PACKET_PAYLOAD	The actual data being transmitted.

Header Breakdown

Bits	Mask	Field	Description
0-1	0x03	Route Type	Specifies the routing type (Flood, Direct, Reserved).
2-5	0x0F	Payload Type	Specifies the type of payload (Request, Response, Text, ACK, etc.).
6-7	0x03	Payload Version	Versioning of the payload format.

Route Type Values

Value	Name	Description
0x00	ROUTE_TYPE_RESERVED1	Reserved for future use.
0x01	ROUTE_TYPE_FLOOD	Flood routing mode (builds up path).
0x02	ROUTE_TYPE_DIRECT	Direct route (path is supplied).
0x03	ROUTE_TYPE_RESERVED2	Reserved for future use.

Payload Type Values

Value	Name	Description
0x00	PAYLOAD_TYPE_REQ	Request (destination/source hashes + MAC).
0x01	PAYLOAD_TYPE_RESPONSE	Response to REQ or ANON_REQ.
0x02	PAYLOAD_TYPE_TXT_MSG	Plain text message.
0x03	PAYLOAD_TYPE_ACK	Acknowledgment.
0x04	PAYLOAD_TYPE_ADVERT	Node advertisement.
0x05	PAYLOAD_TYPE_GRP_TXT	Group text message (unverified).
0x06	PAYLOAD_TYPE_GRP_DATA	Group datagram (unverified).
0x07	PAYLOAD_TYPE_ANON_REQ	Anonymous request.
0x08	PAYLOAD_TYPE_PATH	Returned path.
0x0F	PAYLOAD_TYPE_RAW_CUSTOM	Custom packet (raw bytes, custom encryption).

Payload Version Values

Value	Name	Description
0x00	PAYLOAD_VER_1	1-byte src/dest hashes, 2-byte MAC.
0x01	PAYLOAD_VER_2	Future version (e.g., 2-byte hashes, 4-byte MAC).
0x02	PAYLOAD_VER_3	Future version.
0x03	PAYLOAD_VER_4	Future version.

[mattsains]

this should be hopefully resolved now by #375 and #338