Fix enchant_item button id: varint, not i8 (1.21 container rework)

[atiweb]

Problem

packet_enchant_item (vanilla ServerboundContainerButtonClickPacket) defines its enchantment field — the container button id — as i8. Since the 1.21 container rework the vanilla codec encodes it as a VarInt:

// ServerboundContainerButtonClickPacket, 1.21+
StreamCodec.composite(
  ByteBufCodecs.CONTAINER_ID, ::containerId,   // varint (plain VAR_INT in 1.21.1)
  ByteBufCodecs.VAR_INT,      ::buttonId,      // varint  <-- mcdata still has i8
  ::new)

minecraft-data already updated windowId to ContainerID (varint) for 1.21+, but left enchantment as i8 — an incomplete update of the same packet.

versions	windowId	enchantment (mcdata)	jar button id
≤ 1.20.5	i8	i8 ✓	byte
1.21.1 – 1.21.11	ContainerID	i8 ✗	VarInt

Before 1.21 both fields were a single byte (readByte/writeByte), so i8 is correct there — this only affects 1.21.1 – 1.21.11.

Impact

A VarInt and a byte encode identically for button ids below 128, so it seldom surfaces. But a button id ≥ 128 — e.g. a stonecutter or loom recipe index on a server with a large recipe set — needs a 2-byte VarInt that an i8 writer cannot represent. The packet is serverbound, so this affects any client encoding it.

Verification

Decompiled the official Mojang server jars: readByte/writeByte for both fields in 1.19.4 (pre-rework), and a VAR_INT button id in 1.21.1 (where the rework lands) and 1.21.3 / 1.21.5 / 1.21.6 / 1.21.8 / 1.21.9.

Change

enchantment: i8 → enchantment: varint in packet_enchant_item, for 1.21.1 → 1.21.11. proto.yml edited and protocol.json regenerated with npm run build (16 files, +16/−16; nothing else touched). node compileProtocol.js validate passes for all versions.