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/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: