Add 26.3-pre-3 protocol support

[electronicboy]

Adds 26.3-pre-3 support behind the existing net.md_5.bungee.protocol.snapshot flag, as a single temporary patch to be dropped once upstream lands its own 26.3 support.

MINECRAFT_26_3 holds the snapshot protocol number (0x40000000 | 335), matching what upstream does during a pre-release cycle before flipping it to the release number.

Packet id remaps

Relative to 26.2, 26.3 inserts post_effects into both the configuration and game clientbound tables, swing_animation into the game clientbound table, and, as of pre-3, add_transient_block at game clientbound 0x25. That last one sits low enough to shift almost the whole table, so 25 of the game clientbound packets we register move, on top of the 7 configuration ones.

Serverbound is unaffected for us: the punch/swing shuffle sits in the 0x2E-0x3F window we do not register in, and CustomClickAction at 0x44 is above it.

Every id was derived from the registration order in GameProtocols and ConfigurationProtocols rather than from a protocol summary, and the resulting table sizes (143 game clientbound, 69 game serverbound, 21 configuration clientbound, 10 configuration serverbound) match the release.

CommonPlayerSpawnInfo

The one packet payload change, affecting both Login and Respawn, which embed it:

• gameType: byte -> var int
• previousGameType: byte with a -1 sentinel -> vanilla's OPTIONAL_VAR_INT, where zero means absent and any other value is the id plus one

Both fields are only ever round-tripped by the proxy, never synthesised, so no call site needed to change. This one is easy to miss: a protocol summary renders it as commonPlayerSpawnInfo: CommonPlayerSpawnInfo [STREAM_CODEC], which looks like a pure refactor.

Everything else we parse really is a FriendlyByteBuf to StreamCodec refactor with an identical wire format — including PlayerListItemUpdate, whose new Action id is enum-internal and not serialised, and Team, whose Collection<String> to List<String> change is the same length-prefixed string list as before.

Command argument types

The argument type registry grew from 57 to 62 entries: context_float_provider, context_int_provider and slot_source after loot_modifier, then feature and swing_animation after dialog, which also shifts dialog and uuid. All five are singleton argument types with no payload, so IDS_26_3 adds them as VOID.

Without this, decoding Commands from a 26.3 backend throws:

io.netty.handler.codec.DecoderException: java.lang.ArrayIndexOutOfBoundsException: Index 59 out of bounds for length 57
	at net.md_5.bungee.protocol.packet.Commands$ArgumentRegistry.read(Commands.java:1006)

26.3 likewise adds a post_effects suggestion provider. Those are keyed by name rather than index and SuggestionRegistry.getProvider rejects unknown names outright, so it is registered as a dummy for every version.

Testing

Builds and passes the test suite. Tested against a 26.3-pre-2 client and backend: connecting, moving between servers, and the command tree all work. The pre-2 to pre-3 delta is packet ids only — no payload or registry changes — and has been verified against the registration order but not yet exercised at runtime.