feat(network): packet manager

[Tchips46]

Closes #408

Choices

• Declaration: definePacket<T>(name, { channel?, validate? }), defined in a protocol file shared by client and server. It is exported from @nanoforge-dev/network, so the shared file needs neither /client nor /server.
• Receiving: two ways, both run in the network __run, before ECS (runAfter: ["ecs"]), so not while paused:
  • packets.on(def, (data, info) => …) listeners, which return an unsubscribe function,
  • packets.read(def), the current tick's packets, for systems.
• Sending: packets.send / sendToAll / sendToClient. The payload is typed and sent as JSON, on the definition's channel unless overridden.
• Wire (breaking): every packet starts with [nameLen u8][name]. nameLen = 0 marks a raw sendData packet, still returned by getReceivedPackets().
• Type id: the name itself, with no registration list. Unknown names get one warning, capped at 100 names.
• Safety:
  • every listener runs in its own try/catch,
  • a failed validate drops the packet,
  • two definitions with the same name but another channel or validate throw,
  • raw packets left unread for a whole tick are dropped, so typed-only servers can't be flooded.