Build for Minecraft 26.1, 26.2 and 26.3

Adds the three drops as Stonecutter versions (26.1's jar also accepts
its hotfixes). loom-back-compat already picks the plain Loom for 26.x;
the testmod's remap configurations are only created where there's
something to remap, and the foojay resolver downloads the Java 25
toolchain these versions need.

- 26.3 renamed PoseStack.mulPose(Quaternionfc) to rotate.
- The testmod follows Fabric API's renames: ClientCommands (26.1),
  getClientLevel (26.1) and getConnection (26.2) for waiting on chunks.
- 26.2 replaced Options.hideGui with the HUD's toggle, so the gametest
  toggles it through a helper.

The screenshot gametest passes on 26.1, 26.2 and 26.3, and the bent
limbs match 1.21.11's.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

build.gradle.kts

@@ -22,7 +22,8 @@ val testmod: SourceSet = sourceSets.create("testmod") {
 }
 
 loom {
-    createRemapConfigurations(testmod)
+    // The testmod's mod* configurations; 26.1+ has nothing to remap, and loomx aliases them there.
+    if (!loomx.isUnobfuscated) createRemapConfigurations(testmod)
 
     mods {
         register("saturn_emotes") { sourceSet(sourceSets.main.get()) }