Refactor SPMD job system, add GGX mipmap benchmark

- Replace IJobSPMD with T4-generated, multi-type SPMD job interfaces and wrappers (up to 8 numeric types)
- Extend ISPMD with Cast/BitCast; implement for ScalarLane and WideLane (SIMD-aware)
- Add unary minus, scalar-lane, and lane-scalar operators to Vector2/3/4; improve Select methods
- WideLane now partial with T4-generated Cast/BitCast (SIMD conversions)
- SPMD job Execute now requires unmanaged TLane; update all usages and benchmarks
- Add GGXMipGenerationBenchmark with vectorized and scalar paths, SkiaSharp output
- Update project files: add generated code, SkiaSharp, bump version to 1.3.0
- Misc: fix formatting, method signatures, FreeList logic

Misaki.HighPerformance.Mathematics.SPMD/WideLane.cs

@@ -32,7 +32,7 @@ public static unsafe class WideLane
 }
 
 [StructLayout(LayoutKind.Sequential)]
-public readonly unsafe struct WideLane<TNumber> : ISPMD<WideLane<TNumber>, TNumber>
+public readonly unsafe partial struct WideLane<TNumber> : ISPMD<WideLane<TNumber>, TNumber>
     where TNumber : unmanaged, INumber<TNumber>, IBinaryNumber<TNumber>, IMinMaxValue<TNumber>, IBitwiseOperators<TNumber, TNumber, TNumber>
 {
     private static readonly Vector<TNumber> s_indices;
@@ -301,6 +301,15 @@ public readonly unsafe struct WideLane<TNumber> : ISPMD<WideLane<TNumber>, TNumb
         return value;
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public TOther BitCast<TOther, TOtherNumber>()
+        where TOther : ISPMD<TOther, TOtherNumber>
+        where TOtherNumber : unmanaged, INumber<TOtherNumber>, IBinaryNumber<TOtherNumber>, IMinMaxValue<TOtherNumber>, IBitwiseOperators<TOtherNumber, TOtherNumber, TOtherNumber>
+    {
+        return Unsafe.BitCast<WideLane<TNumber>, TOther>(this);
+    }
+
+
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static WideLane<TNumber> operator +(WideLane<TNumber> a, WideLane<TNumber> b)
     {