Use 10-bit packed preview format and add OCIO LUT regression tests

Renderer / preview:
- Switch the preview/display readback format from F16 to packed
  10-bit RGBA (PixelFormat::U10) to halve GPU->CPU/IPC bandwidth
  while keeping 10-bit panel precision.
- Add U10 support to VideoParams, FFmpeg/OIIO/OCIO utility mappings,
  OpenGL (GL_RGB10_A2), Vulkan (VK_FORMAT_A2B10G10R10_UNORM_PACK32),
  and plugin bit-depth lookups.
- Update preview autocacher comment to reflect the new behavior.

OCIO LUT tests:
- Add four E2E-style ColorLutNode gtests that drive a SolidGenerator
  -> OCIOLutNode graph through NodeTraverser and compare resulting
  pixels on the CPU. They cover forward/inverse transforms and verify
  that switching LUT direction and LUT file updates both the processor
  and the output pixels.

Cleanup:
- Remove a leftover SolidGenerator::Value debug fprintf.
- Capture render worker stderr in RenderWorkerFootageTest for better
  diagnostics.

app/render/framehashcache.cpp

@@ -433,6 +433,8 @@ bool FrameHashCache::SaveCacheFrame(const QString &filename,
 				fmt = QImage::Format_RGB888;
 			}
 			break;
+		case PixelFormat::U10:
+			break;
 		case PixelFormat::U16:
 			if (frame->channel_count() == VideoParams::kRGBAChannelCount) {
 				fmt = QImage::Format_RGBA64_Premultiplied;

app/render/opengl/openglrenderer.cpp

@@ -835,6 +835,11 @@ GLint OpenGLRenderer::GetInternalFormat(PixelFormat format, int channel_layout)
 			return GL_RGBA8;
 		}
 		break;
+	case PixelFormat::U10:
+		if (channel_layout == 4) {
+			return GL_RGB10_A2;
+		}
+		break;
 	case PixelFormat::U16:
 		switch (channel_layout) {
 		case 1:
@@ -884,6 +889,8 @@ GLenum OpenGLRenderer::GetPixelType(PixelFormat format)
 	switch (format) {
 	case PixelFormat::U8:
 		return GL_UNSIGNED_BYTE;
+	case PixelFormat::U10:
+		return GL_UNSIGNED_INT_2_10_10_10_REV;
 	case PixelFormat::U16:
 		return GL_UNSIGNED_SHORT;
 	case PixelFormat::F16:

app/render/previewautocacher.cpp

@@ -688,9 +688,11 @@ RenderTicketWatcher *PreviewAutoCacher::RenderFrame(Node *node,
 		rvp.AddCache(frame_cache);
 	} else {
 		// Preview/display frames are rendered at reduced precision to cut the
-		// GPU->CPU readback and IPC transfer bandwidth in half. The internal
-		// render pipeline stays F32/ACEScg; only the final preview copy is F16.
-		rvp.force_format = PixelFormat::F16;
+		// GPU->CPU readback and IPC transfer bandwidth. The internal render
+		// pipeline stays F32/ACEScg; the final preview copy is packed 10-bit
+		// RGBA (4 bytes/pixel) to preserve 10-bit panel precision while halving
+		// bandwidth compared to F16.
+		rvp.force_format = PixelFormat::U10;
 		rvp.force_channel_count = VideoParams::kRGBAChannelCount;
 	}
 

app/render/videoparams.cpp

@@ -209,6 +209,8 @@ int VideoParams::GetBytesPerChannel(PixelFormat format)
 		break;
 	case PixelFormat::U8:
 		return 1;
+	case PixelFormat::U10:
+		return 0; // packed format, use GetBytesPerPixel instead
 	case PixelFormat::U16:
 	case PixelFormat::F16:
 		return 2;
@@ -221,6 +223,10 @@ int VideoParams::GetBytesPerChannel(PixelFormat format)
 
 int VideoParams::GetBytesPerPixel(PixelFormat format, int channels)
 {
+	if (format == PixelFormat::U10) {
+		// Packed 10-bit RGBA10A2: 4 bytes per RGBA pixel regardless of channel count
+		return channels == VideoParams::kRGBAChannelCount ? 4 : 0;
+	}
 	return GetBytesPerChannel(format) * channels;
 }
 
@@ -238,6 +244,8 @@ QString VideoParams::GetFormatName(PixelFormat format)
 	switch (format) {
 	case PixelFormat::U8:
 		return QCoreApplication::translate("VideoParams", "8-bit");
+	case PixelFormat::U10:
+		return QCoreApplication::translate("VideoParams", "10-bit Packed");
 	case PixelFormat::U16:
 		return QCoreApplication::translate("VideoParams", "16-bit Integer");
 	case PixelFormat::F16:

app/render/vulkan/vulkanrenderer.cpp

@@ -1127,6 +1127,11 @@ VkFormat VulkanRenderer::PixelFormatToVkFormat(PixelFormat format,
 		case 4: return VK_FORMAT_R8G8B8A8_UNORM;
 		}
 		break;
+	case PixelFormat::U10:
+		if (channel_count == 4) {
+			return VK_FORMAT_A2B10G10R10_UNORM_PACK32;
+		}
+		break;
 	case PixelFormat::U16:
 		switch (channel_count) {
 		case 1: return VK_FORMAT_R16_UNORM;
@@ -1203,6 +1208,8 @@ int VulkanRenderer::GetVkFormatBytesPerPixel(VkFormat format) const
 		return 3;
 	case VK_FORMAT_R8G8B8A8_UNORM:
 		return 4;
+	case VK_FORMAT_A2B10G10R10_UNORM_PACK32:
+		return 4;
 	case VK_FORMAT_R16_UNORM:
 	case VK_FORMAT_R16_SFLOAT:
 		return 2;