Upgrade to OpenUSD 25.11 (Python 3.12) and fix Arnold/Embree regressions

Build against OpenUSD 25.11 built from source with Python 3.12, OCIO 2.2.1,
OpenVDB, Ptex and Embree, replacing the 25.05/py311 mix.

Build system:
- CMAKE_PREFIX_PATH -> third_party/OpenUSD-v25.11; HDARNOLD_ROOT ->
  hdArnold-v25.11. hdEmbree is bundled in the USD build now, so
  HDEMBREE_USD_ROOT is no longer needed.
- FindOpenUSD: drop usd_ndr (ndr was merged into sdr in 25.11).
- hdArnold plugin renames: ndrArnold -> nodeRegistryArnold, plus the new
  usdImagingArnold plugin.
- Glob the version-suffixed OpenColorIO_*.dll instead of hardcoding 2_1.
- Drop the python311.dll workaround; USD and Cycles now share Python 3.12.
- Cycles: deploy OpenColorIO_2_5.dll (needed by its bundled OpenImageIO) and
  stop the debug-DLL filter from eating IlmThread.dll -- the regex `d[.]dll$`
  also matched legitimate Release DLLs.

Runtime fixes:
- cullStyle now defaults to Nothing, matching usdview (viewSettingsDataModel
  cullBackfaces=False). BackUnlessDoubleSided drops back faces on geometry
  that isn't authored doubleSided, which hdEmbree applies to occlusion rays
  too, so interiors shaded as single-sided.
- Set HDARNOLD_osl_includepath (and PXR_MTLX_STDLIB_SEARCH_PATHS) in main.cpp
  before the plugin DLL pre-load. hdArnold compiles MaterialX via generated
  OSL that begins with #include "mx_funcs.h"; without an include path Arnold
  fails with "fatal error: 'mx_funcs.h' file not found". It must be set before
  any plugin loads because TF_DEFINE_ENV_SETTING caches the value when
  hdArnold.dll registers its settings.
- Deploy the MaterialX standard library next to the executable.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CMakePresets.json

@@ -9,15 +9,14 @@
       "binaryDir": "${sourceDir}/build",
       "cacheVariables": {
         "CMAKE_INSTALL_PREFIX": "${sourceDir}/install",
-        "CMAKE_PREFIX_PATH": "${sourceDir}/third_party/OpenUSD-v25.05",
+        "CMAKE_PREFIX_PATH": "${sourceDir}/third_party/OpenUSD-v25.11",
         "IMGUI_DIR": "${sourceDir}/third_party/imgui-1.92.7",
         "CMAKE_CXX_STANDARD": "17",
         "CMAKE_CXX_STANDARD_REQUIRED": "ON",
         "BUILD_TESTS": "OFF",
         "WITH_CYCLES": "ON",
-        "HDARNOLD_ROOT": "E:/library/hdArnold",
-        "ARNOLD_LOCATION": "C:/Autodesk/mtoa/5.5.0/2026",
-        "HDEMBREE_USD_ROOT": "E:/USD_v25.05_embree"
+        "HDARNOLD_ROOT": "E:/library/hdArnold-v25.11",
+        "ARNOLD_LOCATION": "C:/Autodesk/mtoa/5.5.0/2026"
       }
     },
     {