Fix Spigot 1.21.10+ ReflServerStateProvider

[Stackulate]

Information

This PR fixes #6376.

Details

Proposed fix:

Added NMS Versions v1_21_R6 and v1_21_R7 and their respective ReflServerStateProvider MDFIVEMAGICLETTER.

Environments tested:

OS: Ubuntu 24.04

Java version: 25.0.1

• [ ] Most recent Paper version (1.XX.Y, git-Paper-BUILD)
• [ ] CraftBukkit/Spigot/Paper 1.12.2
• [ ] CraftBukkit 1.8.8

Demonstration:

The console error (see https://essentialsx.net/dump.html?bytebin=TFXJgqbAfF) no longer appears when EssentialsX is enabled on Spigot 1.21.10+.