Remove crafty namespace from solver

Solver/ArenaBuffer.cs

@@ -0,0 +1,41 @@
+using System.Diagnostics.Contracts;
+using System.Numerics;
+using System.Runtime.CompilerServices;
+
+namespace Craftimizer.Solver;
+
+// Adapted from https://github.com/dtao/ConcurrentList/blob/4fcf1c76e93021a41af5abb2d61a63caeba2adad/ConcurrentList/ConcurrentList.cs
+public struct ArenaBuffer<T> where T : struct
+{
+    // Technically 25, but it's very unlikely to actually get to there.
+    // The benchmark reaches 20 at most, but here we have a little leeway just in case.
+    private const int MaxSize = 24;
+
+    private static readonly int BatchSize = Vector<float>.Count;
+    private static readonly int BatchSizeBits = int.Log2(BatchSize);
+    private static readonly int BatchSizeMask = BatchSize - 1;
+
+    private static readonly int BatchCount = MaxSize / BatchSize;
+
+    public ArenaNode<T>[][] Data;
+    public int Count { get; private set; }
+
+    public void Add(ArenaNode<T> node)
+    {
+        Data ??= new ArenaNode<T>[BatchCount][];
+
+        var idx = Count++;
+
+        var (arrayIdx, subIdx) = GetArrayIndex(idx);
+
+        Data[arrayIdx] ??= new ArenaNode<T>[BatchSize];
+
+        node.ChildIdx = (arrayIdx, subIdx);
+        Data[arrayIdx][subIdx] = node;
+    }
+
+    [Pure]
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static (int arrayIdx, int subIdx) GetArrayIndex(int idx) =>
+        (idx >> BatchSizeBits, idx & BatchSizeMask);
+}