Return scalar MulMod results and benchmark native reducers

EvenPerfectBitScanner.Benchmarks/GpuUInt128ScalarMulModBenchmarks.cs

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+using System.Collections.Generic;
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Jobs;
+using PerfectNumbers.Core.Gpu;
+
+namespace EvenPerfectBitScanner.Benchmarks;
+
+[SimpleJob(RuntimeMoniker.Net80)]
+[MemoryDiagnoser]
+public class GpuUInt128ScalarMulModBenchmarks
+{
+    private static readonly ScalarMulModInput[] Inputs = new ScalarMulModInput[]
+    {
+        new(
+            new GpuUInt128(0x0000_0000_0000_0000UL, 0x0000_0000_0000_0011UL),
+            0x0000_0000_0000_0013UL,
+            new GpuUInt128(0x0000_0000_0000_0001UL, 0x0000_0000_0000_00FFUL),
+            "TinyOperands"),
+        new(
+            new GpuUInt128(0x0123_4567_89AB_CDEFUL, 0xFEDC_BA98_7654_3210UL),
+            0x0F1E_2D3C_4B5A_6978UL,
+            new GpuUInt128(0x0FFF_FFFF_FFFF_FFFFUL, 0xFFFF_FFFF_FFFF_FFC3UL),
+            "MixedMagnitude"),
+        new(
+            new GpuUInt128(0x8000_0000_0000_0000UL, 0x0000_0000_0000_0001UL),
+            0x7FFF_FFFF_FFFF_FFFBUL,
+            new GpuUInt128(0x7FFF_FFFF_FFFF_FFFFUL, 0xFFFF_FFFF_FFFF_FFF1UL),
+            "HighWordDominant"),
+    };
+
+    [ParamsSource(nameof(GetInputs))]
+    public ScalarMulModInput Input { get; set; }
+
+    public static IEnumerable<ScalarMulModInput> GetInputs() => Inputs;
+
+    [Benchmark(Baseline = true)]
+    public GpuUInt128 StructAllocating()
+    {
+        GpuUInt128 value = Input.Left;
+        value.MulMod(new GpuUInt128(Input.Right), Input.Modulus);
+        return value;
+    }
+
+    [Benchmark]
+    public GpuUInt128 SpecializedScalar()
+    {
+        GpuUInt128 value = Input.Left;
+        value.MulMod(Input.Right, Input.Modulus);
+        return value;
+    }
+
+    public readonly record struct ScalarMulModInput(GpuUInt128 Left, ulong Right, GpuUInt128 Modulus, string Name)
+    {
+        public override string ToString() => Name;
+    }
+}
+