Refactor SPMD lane abstraction and add gather support

- Rename ISPMD interfaces to ISPMDLane for clarity
- Add gather and mask load methods to ISPMDLane, implement for ScalarLane and WideLane
- Add GetUnsafePtr() for direct pointer access
- Update MathV and vector types to use new interface and gather methods
- Update SPMD job interfaces and implementations to ISPMDLane
- Improve hash codes, range checks, and safety checks in vector types
- Update codegen templates for new interface/methods
- Refactor SPMD jobs to use gather methods for efficient vectorized access

Misaki.HighPerformance.Mathematics.SPMD/Templates/Vector4.gen.cs

@@ -6,7 +6,7 @@ using System.Runtime.CompilerServices;
 namespace Misaki.HighPerformance.Mathematics.SPMD;
 
 public unsafe struct Vector4<TLane, TNumber> : IEquatable<Vector4<TLane, TNumber>>
-    where TLane : ISPMD<TLane, TNumber>
+    where TLane : ISPMDLane<TLane, TNumber>
     where TNumber : unmanaged, INumber<TNumber>, IBinaryNumber<TNumber>, IMinMaxValue<TNumber>, IBitwiseOperators<TNumber, TNumber, TNumber>
 {
     public TLane x;
@@ -55,12 +55,12 @@ public unsafe struct Vector4<TLane, TNumber> : IEquatable<Vector4<TLane, TNumber
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    [Conditional("ENABLE_COLLECTION_CHECKS")]
+    [Conditional("MHP_ENABLE_SAFETY_CHECKS")]
     private static void RangeCheck(int index)
     {
         if (index < 0 || index >= 4)
         {
-            throw new IndexOutOfRangeException($"Index {index} is out of range for Vector2.");
+            throw new IndexOutOfRangeException($"Index {index} is out of range for Vector4.");
         }
     }
 
@@ -498,8 +498,13 @@ public unsafe struct Vector4<TLane, TNumber> : IEquatable<Vector4<TLane, TNumber
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public override int GetHashCode()
+    public override readonly int GetHashCode()
     {
-        throw new NotImplementedException();
+        var hash = new HashCode();
+        hash.Add(x);
+        hash.Add(y);
+        hash.Add(z);
+        hash.Add(w);
+        return hash.ToHashCode();
     }
 }