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/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;