Refactor SPMD jobs for true vectorized/masked execution

- Change IJobSPMD.Execute to (indices, mask, ctx) signature for all arities, enabling proper vectorized/masked SPMD execution.
- Update all SPMD job wrappers, extension methods, and test jobs to use new interface.
- Add AVX2 gather/masked gather support to MathV.GatherVector2/3/4 and related methods; use [ConstantExpected] byte scale.
- Improve gather/select logic, pointer arithmetic, and overloads for ref/int* index access.
- Refactor GGXMipGenerationBenchmark and jobs for SPMD, with per-mip-level vectorized jobs and improved memory access.
- Clean up code, fix naming, update comments, and bump version to 1.3.6.

Misaki.HighPerformance.Mathematics.SPMD/Templates/Vector3.gen.cs

@@ -89,7 +89,7 @@ public unsafe struct Vector3<TLane, TNumber> : IEquatable<Vector3<TLane, TNumber
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void Store(TNumber* px,  TNumber* py,  TNumber* pz)
+    public void Store(TNumber* px, TNumber* py, TNumber* pz)
     {
         x.Store(px);
         y.Store(py);
@@ -97,7 +97,7 @@ public unsafe struct Vector3<TLane, TNumber> : IEquatable<Vector3<TLane, TNumber
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void Store(ref TNumber x,  ref TNumber y,  ref TNumber z)
+    public void Store(ref TNumber x, ref TNumber y, ref TNumber z)
     {
         this.x.Store(ref x);
         this.y.Store(ref y);