Bend limbs along a single axis with a Bézier spine

- core: Bezier (any degree, De Casteljau), LimbBend (cubic spine through
  the rigid upper/joint/lower shape, one ring per texture row spaced by
  arc length, rigid rings so pieces share vertices) and QuadSplitter
  (cuts faces at the rings, interpolating UVs).
- fabric: ModelPartMixin draws parts that have a bend with
  BentCubeRenderer, which deforms vanilla's own cubes. Overlays and armor
  use the limb's spine so they stay attached. Bends are reset every
  setupAnim because models are shared between entities.
- testmod: flap and squat animations, and a client gametest that
  screenshots each animation from the front and side
  (runClientGameTest). The tester runs with the full Fabric API because
  single modules don't bring their version-specific dependencies.

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

build.gradle.kts

@@ -33,6 +33,13 @@ loom {
         options.put("mark-corresponding-synthetics", "1") // Names lambdas, useful for mixins
     }
 
+    runConfigs.all {
+        preferGradleTask = true
+        generateRunConfig = true
+        runDirectory = rootProject.file("run") // Shared by every version
+        jvmArguments.add("-Dmixin.debug.export=true")
+    }
+
     runs {
         // ./gradlew :<mc>:runTestmodClient launches the game with the tester mod loaded.
         register("testmodClient") {
@@ -40,13 +47,15 @@ loom {
             name = "Testmod Client"
             source(testmod)
         }
-    }
 
-    runConfigs.all {
-        preferGradleTask = true
-        generateRunConfig = true
-        runDirectory = rootProject.file("run") // Shared by every version
-        jvmArguments.add("-Dmixin.debug.export=true")
+        // ./gradlew :<mc>:runClientGameTest screenshots the test animations, then quits.
+        register("clientGameTest") {
+            client()
+            name = "Client Game Test"
+            source(testmod)
+            vmArg("-Dfabric.client.gametest")
+            runDir = "build/run/clientGameTest"
+        }
     }
 }
 
@@ -65,7 +74,12 @@ dependencies {
     api(project(":core"))
     include(project(":core"))
 
-    "modTestmodImplementation"(fabricApi.module("fabric-command-api-v2", sc.properties["deps.fabric_api"]))
+    for (module in listOf("fabric-command-api-v2", "fabric-client-gametest-api-v1")) {
+        "modTestmodImplementation"(fabricApi.module(module, sc.properties["deps.fabric_api"]))
+    }
+    // Single modules don't bring their Fabric API dependencies (which differ between versions),
+    // so the tester runs with all of Fabric API.
+    "modTestmodRuntimeOnly"("net.fabricmc.fabric-api:fabric-api:${sc.properties.get<String>("deps.fabric_api")}")
 }
 
 java {