Add Fabric support for 1.21.10 through 26.2

[alexdev03]

Summary

• add Fabric support for Minecraft 1.21.10, 1.21.11, 26.1.2, and 26.2
• adapt custom payload/network handling for the 26.x API and mappings
• keep the mod server-only while packaging required Placeholder API and Adventure dependencies
• relocate Lettuce's bundled Netty classes to avoid collisions with Minecraft's Netty version
• update the Gradle/Essential tooling required by the new versions

Verification

• ./gradlew :fabric:1.21.10:build :fabric:1.21.11:build :fabric:26.1.2:shadowJar :fabric:26.2:shadowJar --no-daemon --console=plain
• production Fabric dedicated server boot with Fabric Loader 0.19.3 on every target
• real offline client connection on every target, without PAPIProxyBridge loaded client-side
• Redis request/response parsing through PAPIProxyBridge on every target:
  • 1.21.10: PAPI=confirmed PLAYER=PAPISmoke ONLINE=1
  • 1.21.11: PAPI=confirmed PLAYER=PAPISmoke ONLINE=1
  • 26.1.2: PAPI=confirmed PLAYER=PAPISmoke ONLINE=1
  • 26.2: PAPI=confirmed PLAYER=PAPISmoke ONLINE=1
• all four server logs contained successful enable/join events and zero errors
• artifact metadata verified as environment: server with only the server entrypoint