phase(N.5) Task 3: TextureCache bindless GetOrUpload + parallel cache

Adds three Bindless variants (GetOrUploadBindless,
GetOrUploadWithOrigTextureOverrideBindless,
GetOrUploadWithPaletteOverrideBindless) that decode + upload via
UploadRgba8AsLayer1Array (Texture2DArray) and cache in three new
dictionaries that mirror the legacy three-cache structure. Each entry
stores both the GL texture name (for Dispose cleanup in Task 4) and
the resident bindless handle.

Constructor gains optional BindlessSupport param; null keeps backward
compat. EnsureBindlessAvailable throws InvalidOperationException if
Bindless* methods are called without BindlessSupport (fail-fast vs
silent zero handle that would produce GPU faults).

Dispose extended to make handles non-resident before deleting the
underlying Texture2DArray names (bindless handles must be made
non-resident before the texture is deleted; skipping this causes
GPU faults on driver cleanup).

Marker test in TextureCacheBindlessTests documents the throw contract
for future engineers; real bindless integration is verified at
Task 14's visual gate.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/AcDream.Core.Tests/Rendering/TextureCacheBindlessTests.cs

@@ -0,0 +1,32 @@
+using AcDream.App.Rendering;
+using AcDream.App.Rendering.Wb;
+using DatReaderWriter;
+using Xunit;
+
+namespace AcDream.Core.Tests.Rendering;
+
+/// <summary>
+/// Lightweight unit tests for <see cref="TextureCache"/>'s bindless path.
+/// We can't construct a real TextureCache in a headless test (it requires a
+/// live GL context), so this file documents contracts that future engineers
+/// should preserve. Real bindless integration is verified at Task 14's
+/// visual gate.
+/// </summary>
+public sealed class TextureCacheBindlessTests
+{
+    [Fact]
+    public void Contract_BindlessMethodsThrowWithoutBindlessSupport()
+    {
+        // The actual throw lives in TextureCache.EnsureBindlessAvailable
+        // and is reached only via GL-bound Bindless* method calls. The
+        // contract is: if the dispatcher (which requires bindless) ever
+        // gets a TextureCache constructed without BindlessSupport, it
+        // should fail-fast with InvalidOperationException — NOT silently
+        // route a draw to handle 0 (which would produce a non-resident
+        // GPU fault).
+        //
+        // This test is a marker. Future engineers: do not weaken
+        // EnsureBindlessAvailable to swallow the missing dependency.
+        Assert.True(true, "Contract documented in TextureCache.EnsureBindlessAvailable");
+    }
+}