Refactor V2 animation, furniture, and GLTF rendering

Broad consolidation of the V2 bondage-item, furniture-entity, and
client-side GLTF pipeline.

Parsing and rendering
  - Shared GLB parsing helpers consolidated into GlbParserUtils
    (accessor reads, weight normalization, joint-index clamping,
    coordinate-space conversion, animation parse, primitive loop).
  - Grow-on-demand Matrix4f[] scratch pool in GltfSkinningEngine and
    GltfLiveBoneReader — removes per-frame joint-matrix allocation
    from the render hot path.
  - emitVertex helper dedups three parallel loops in GltfMeshRenderer.
  - TintColorResolver.resolve has a zero-alloc path when the item
    declares no tint channels.
  - itemAnimCache bounded to 256 entries (access-order LRU) with
    atomic get-or-compute under the map's monitor.

Animation correctness
  - First-in-joint-order wins when body and torso both map to the
    same PlayerAnimator slot; duplicate writes log a single WARN.
  - Multi-item composites honor the FullX / FullHeadX opt-in that
    the single-item path already recognized.
  - Seat transforms converted to Minecraft model-def space so
    asymmetric furniture renders passengers at the correct offset.
  - GlbValidator: IBM count / type / presence, JOINTS_0 presence,
    animation channel target validation, multi-skin support.

Furniture correctness and anti-exploit
  - Seat assignment synced via SynchedEntityData (server is
    authoritative; eliminates client-server divergence on multi-seat).
  - Force-mount authorization requires same dimension and a free
    seat; cross-dimension distance checks rejected.
  - Reconnection on login checks for seat takeover before re-mount
    and force-loads the target chunk for cross-dimension cases.
  - tiedup_furniture_lockpick_ctx carries a session UUID nonce so
    stale context can't misroute a body-item lockpick.
  - tiedup_locked_furniture survives death without keepInventory
    (Forge 1.20.1 does not auto-copy persistent data on respawn).

Lifecycle and memory
  - EntityCleanupHandler fans EntityLeaveLevelEvent out to every
    per-entity state map on the client.
  - DogPoseRenderHandler re-keyed by UUID (stable across dimension
    change; entity int ids are recycled).
  - PetBedRenderHandler, PlayerArmHideEventHandler, and
    HeldItemHideHandler use receiveCanceled + sentinel sets so
    Pre-time mutations are restored even when a downstream handler
    cancels the render.

Tests
  - JUnit harness with 76+ tests across GlbParserUtils, GltfPoseConverter,
    FurnitureSeatGeometry, and FurnitureAuthPredicate.

build.gradle

@@ -231,11 +231,30 @@ dependencies {
     // The group id is ignored when searching -- in this case, it is "blank"
     // implementation fg.deobf("blank:coolmod-${mc_version}:${coolmod_version}")
 
+    // Unit tests (pure-logic, no Minecraft runtime).
+    // Do NOT add Forge/Minecraft dependencies here — the test classpath is intentionally
+    // kept minimal so tests run fast and are isolated from the mod environment.
+    // Tests that need MC runtime should use the Forge GameTest framework instead.
+    testImplementation 'org.junit.jupiter:junit-jupiter:5.10.2'
+    testImplementation 'org.mockito:mockito-core:5.11.0'
+    testRuntimeOnly 'org.junit.platform:junit-platform-launcher:1.10.2'
+
     // For more info:
     // http://www.gradle.org/docs/current/userguide/artifact_dependencies_tutorial.html
     // http://www.gradle.org/docs/current/userguide/dependency_management.html
 }
 
+// JUnit 5 test task configuration.
+// ForgeGradle's default `test` task does not enable JUnit Platform by default — we
+// must opt-in explicitly for the Jupiter engine to discover @Test methods.
+tasks.named('test', Test).configure {
+    useJUnitPlatform()
+    testLogging {
+        events 'passed', 'skipped', 'failed'
+        showStandardStreams = false
+    }
+}
+
 // This block of code expands all declared replace properties in the specified resource targets.
 // A missing property will result in an error. Properties are expanded using ${} Groovy notation.
 // When "copyIdeResources" is enabled, this will also run before the game launches in IDE environments.