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/Vector{T}Helper.ttinclude

@@ -114,13 +114,13 @@ public unsafe struct {typeName} : IEquatable<{typeName}>
     }}
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void Store({ForEachDimension(dimension, 1, ", ", (dim, sb) => sb.Append($"{TNumber}* p{components[dim]}"), false)})
+    public void Store({ForEachDimension(dimension, 1, ",", (dim, sb) => sb.Append($"{TNumber}* p{components[dim]}"), false)})
     {{
 {ForEachDimension(dimension, 8, Environment.NewLine, (dim, sb) => sb.Append($"{components[dim]}.Store(p{components[dim]});"))}
     }}
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void Store({ForEachDimension(dimension, 1, ", ", (dim, sb) => sb.Append($"ref {TNumber} {components[dim]}"), false)})
+    public void Store({ForEachDimension(dimension, 1, ",", (dim, sb) => sb.Append($"ref {TNumber} {components[dim]}"), false)})
     {{
 {ForEachDimension(dimension, 8, Environment.NewLine, (dim, sb) => sb.Append($"this.{components[dim]}.Store(ref {components[dim]});"))}
     }}