Support Minecraft 26.1.2 and 26.2

Adds the v26_1_R1 binding, which covers both versions. 26.x servers are
not obfuscated and need Java 25, so the build moves to Gradle 9.5.1 and
paperweight-userdev 2.0.0-beta.21, and the binding compiles against the
26.1.2 dev bundle with a Java 25 toolchain while everything else stays on
Java 21.

On 26.x every world is a dimension inside the main level, so the binding
provides DimensionWorldStorage:
- world folders resolve to <level>/dimensions/<namespace>/<key>
- data packs go to the level's datapacks folder
- Iris data in a pre-26.1 world folder is moved into the dimension
  before Paper imports the world and deletes the old folder
- "main=true" swaps the world in as the level's overworld instead of
  changing level-name

Also:
- INMS compares 1.x and 26.x versions in release order
- data pack formats 101 (26.1.2) and 107 (26.2), declared with
  min_format/max_format from format 82 on
- dimension types get the fields 26.1 added
- the Java safeguard accepts Java 25

Model used: Claude Opus 5.5

buildSrc/build.gradle.kts

@@ -27,6 +27,6 @@ repositories {
 dependencies {
     implementation("org.ow2.asm:asm:9.8")
     implementation("com.github.VolmitSoftware:NMSTools:c88961416f")
-    implementation("io.papermc.paperweight:paperweight-userdev:2.0.0-beta.18")
+    implementation("io.papermc.paperweight:paperweight-userdev:2.0.0-beta.21")
     implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.10.2")
 }