Fix handshake hostname length limit and plugin message drop during join

[SendableMetatype]

• Remove restrictive handshake hostname length limit: The 261-character MAXIMUM_HOSTNAME_LENGTH in HandshakePacket.decode() silently disconnects clients when enough plugins inject forwarding data into the hostname field that the combined length exceeds the limit. readString(buf) now uses the default 65536 limit, matching every other string field and aligning with Paper/Spigot's equivalent fix (readUtf(255) to readUtf(Short.MAX_VALUE) in ClientIntentionPacket).

• Fix plugin messages silently dropped during player join: Fixes Plugin messages silently dropped during player join when getConnectedServer() is null #1766