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/VoxelDensityOpStack.cpp

@@ -7504,7 +7504,7 @@ namespace
             if (!(DistFromSurface < LineRange)) { return; }
 
             const float LinePhase = WorldZ * (2.0f * PI) / LP.LayerLineSpacing;
-            float LineValue = FMath::Sin(LinePhase);
+            float LineValue = VoxelMath::DetSin(LinePhase);
 
             LineValue = FMath::Max(LineValue, 0.0f);
             LineValue = LineValue * LineValue * LineValue;   // affûtage cubique
@@ -7606,7 +7606,7 @@ namespace
             if (!(DistFromSurface < RibRange)) { return; }
 
             const float RibPhase = WorldZ * (2.0f * PI) / LP.RibbingSpacing + PI * 0.5f;
-            float RibValue = FMath::Sin(RibPhase);
+            float RibValue = VoxelMath::DetSin(RibPhase);
 
             RibValue = FMath::Max(RibValue, 0.0f);
             RibValue = RibValue * RibValue;   // profil de bosse arrondi