fix(determinism): own sin/cos on the world path -- same world on every CPU, 3.5% faster

On Win64, FMath::Sin/Cos resolve to CRT sinf/cosf (GenericPlatformMath.h:521/530; no platform
override), and the UCRT picks FMA3 or non-FMA3 implementations at startup by CPU. /fp:precise
closed only the compiler half, so the same build and seed could build a slightly different world
on two Windows PCs, and on Linux.

- VoxelMath::DetSin/DetCos/DetSinCos (VoxelTypes.h): fixed double-precision period reduction to
  a quarter period, then fixed float minimax polynomials; no CRT, FMath or CPU-dependent
  intrinsic. Measured max error vs sinf 5.96e-8 over the used range (|arg| <= 6.19).
- Every world-deciding FMath::Sin/Cos replaced (generator, op stacks, cave morphology, strate
  manager, content placement, strate measure); none remain in runtime code.
- Pinned test VoxelForge.Determinism.DetSinCos (golden bit patterns + error bound).
- Diagnostic start-up switch -voxel.CrtFma3=0 (Windows) forces the CRT's non-FMA3 path.
- Parse-once console switches now initialise in StartupModule on the game thread; workers only
  read them (was an unsynchronised first parse inside GetDensityAt).
- Corrected the CRC comment that claimed a CRC32 cannot give a false positive.

Proof (Codex round; orchestrator re-checked):
- Before the fix, FMA3 on vs off was identical on this Ryzen 7 5800X3D: the hole exists but was
  not observed in this world. After the fix, the canonical exports are byte-identical with
  FMA3 on and off.
- The world changed once, as expected. New canonical export SHA-256 CBB8AE18...906F (geometry
  B9EF84AC; was B3E5F4C3...377); worms region 9242C093 (was 311CA42C), walk OBJ 20CCF7BD....
  Triangle counts unchanged in every tile. Order-independent nearest-vertex distance, worms
  region: max 8.7 micrometres (the reported "11.4 m" was a line-order artefact of a line-by-line
  OBJ diff); export region max 3e-5 m.
- Capability exact: player-fit 20,830, walk-reachable 10,909, connected. TilePostReachProof,
  sealed-proof, cross-platform and strate-crossing tests pass.
- Performance, headless game path, S/M/S/M vs the committed-tip DLL: static worker 27.41 s vs
  28.44 s (-3.6%), moving 59.59 s vs 61.74 s (-3.5%); LOD0 p50/p95 not worse.

From Sol's code review (DESIGN-SOL-2026-09-15-CODE.md, section 4.1), branch sol/deterministic-math.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TaFdXhTdYMkW1xrV6ApT6Y

Source/VoxelForge/Private/Tests/VoxelForgePassageOpenSpaceTest.cpp

@@ -963,8 +963,10 @@ bool FVoxelForgePassageLandsInOpenSpaceTest::RunTest(const FString& Parameters)
         for (int32 RingSample = 0; RingSample < RingSampleCount; ++RingSample)
         {
             const float Angle = 2.0f * PI * (float)RingSample / (float)RingSampleCount;
-            const float SampleX = Passage.LowerPoint.X + FMath::Cos(Angle) * RingRadius;
-            const float SampleY = Passage.LowerPoint.Y + FMath::Sin(Angle) * RingRadius;
+            float SinAngle = 0.0f, CosAngle = 0.0f;
+            VoxelMath::DetSinCos(SinAngle, CosAngle, Angle);
+            const float SampleX = Passage.LowerPoint.X + CosAngle * RingRadius;
+            const float SampleY = Passage.LowerPoint.Y + SinAngle * RingRadius;
             const float Density = World.Generator->GetDensityAt(
                 SampleX,
                 SampleY,
@@ -1115,7 +1117,7 @@ bool FVoxelForgePassageLandsInOpenSpaceTest::RunTest(const FString& Parameters)
                 LandingGradient = MaxGradient;
                 WorstLandingFloorGradient = FMath::Max(WorstLandingFloorGradient, MaxGradient);
                 const float NormalZ = 1.0f / FMath::Sqrt(1.0f + MaxGradient * MaxGradient);
-                bFloorPassed = NormalZ + KINDA_SMALL_NUMBER >= FMath::Cos(
+                bFloorPassed = NormalZ + KINDA_SMALL_NUMBER >= VoxelMath::DetCos(
                     FMath::DegreesToRadians(LandingWalkableAngleDegrees));
             }