Add Embree 4.4.1 C# bindings

[jcant0n]

Low-level P/Invoke bindings for Intel Embree 4.4.1,
following the Evergine binding pattern: a CppAst-based generator parses the vendored Embree
headers and emits the .cs files that make up Evergine.Bindings.Embree.

What is generated

153 functions, 13 enums, 35 structs, 15 function-pointer typedefs and 7 opaque handle types,
split into Constants.cs, Enums.cs, Delegates.cs, Handles.cs, Structs.cs and
Functions.cs. The full C API is covered: devices, scenes, all geometry types, ray queries
(1/4/8/16 plus the Traversable and Forward variants), point queries, the BVH builder and
every callback.

Points worth reviewing

• Deterministic parsing. The generator runs in C mode against stub system headers in
  EmbreeGen/Headers/stubs and a pinned x86_64-pc-windows target, so the output is identical
  on a Windows dev box and on the linux-x64 CI runner. Without the stubs it picked up whatever
  MSVC or libc headers the machine happened to have.
• rtcore_config.h is vendored. CMake generates it and it decides the layout of several
  public structs (RTC_MAX_INSTANCE_LEVEL_COUNT, RTC_GEOMETRY_INSTANCE_ARRAY,
  RTC_MIN_WIDTH). The native build workflow uploads it next to the binaries so the two cannot
  drift; HelloEmbree asserts the resulting struct sizes at startup.
• Explicit StructLayout.Size. Embree declares most structs RTC_ALIGN(16/32/64), which
  rounds their C sizeof up: RTCHit has 36 bytes of fields but is 48 bytes wide. A plain
  sequential C# struct would be narrower and RTCRayHit would be laid out wrong, so generated
  structs carry the size clang computed.
• RTC_FORCEINLINE helpers. They have no exported symbol, so the generator skips them and
  hand-written equivalents live in Embree.Inline.cs, together with the SoA RayN_*/HitN_*
  packet accessors from the C++ section of rtcore_ray.h.
• C bool maps to byte, not bool: the default .NET marshalling of bool is the 4-byte
  Win32 BOOL, not the 1-byte C _Bool.
• A module initializer registers a DllImport resolver so project references behave like the
  NuGet package.

Samples

• HelloEmbree — console smoke test: asserts struct sizes, then runs rtcIntersect1 and
  rtcOccluded1 against a triangle.
• HelloEmbree.Evergine — CPU ray tracer drawn through the Evergine low-level graphics API,
  hosted in a Windows Forms window, with a --bench mode reporting per-stage cost.

One thing this surfaced that is worth knowing when using the binding: RTCRay and RTCRayHit
must be 16-byte aligned. Embree's kernels use aligned SIMD loads and a C# local carries no such
guarantee, so &someLocal crashes on some code paths and silently works on others. Both samples
allocate rays with NativeMemory.AlignedAlloc, and the READMEs call it out.

Not done yet

• No native binaries. runtimes/ only has .gitkeep. They are produced by the manually
  dispatched Build Embree Libraries workflow (EMBREE_TASKING_SYSTEM=INTERNAL, so each binary
  is self-contained with no TBB dependency) and have to be committed together with the
  rtcore_config.h from the same build. Until then neither sample runs from a fresh clone.
• win-arm64 is untested. Its windows-11-arm runner leg may need toolchain adjustments; if
  it does not work, dropping that RID from the first release and from the README is reasonable.
• Verified locally against the official Intel embree4.dll for win-x64, whose rtcore_config.h
  matches the vendored one exactly.