update to Paper 26.3: load biome colors from vanilla data, fix dappled forest grass

Biome grass/foliage/dry-foliage/water colors and grass color modifiers are now
read from the server's built-in worldgen biome data at runtime, with a 26.3
snapshot as fallback. Fixes missing biomes (dappled_forest, pale_garden,
sulfur_caves) and several outdated values. Replace deprecated ExactChoice
constructors.

build.gradle

@@ -19,7 +19,7 @@ repositories {
 }
 
 dependencies {
-    compileOnly("io.papermc.paper:paper-api:26.2.build.129-stable")
+    compileOnly("io.papermc.paper:paper-api:26.3.build.240-stable")
 }
 
 def targetJavaVersion = 25