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/node/generator/solid/solid.cpp

@@ -66,10 +66,6 @@ void SolidGenerator::Value(const NodeValueRow &value,
 						   const NodeGlobals &globals,
 						   NodeValueTable *table) const
 {
-	Color c = value[kColorInput].toColor();
-	fprintf(stderr,
-			"SolidGenerator::Value color=%f %f %f %f\n",
-			c.red(), c.green(), c.blue(), c.alpha());
 	table->Push(NodeValue::kTexture,
 				Texture::Job(globals.vparams(), ShaderJob(value)), this);
 }