test: add benchmarks for Flatten and Flatten2 functions

Author: ToeiRei

util/slicest/slices_benchmark_test.go

@@ -0,0 +1,62 @@
+// Copyright (c) 2026 Keymaster Team
+// Keymaster - SSH key management system
+// This source code is licensed under the MIT license found in the LICENSE file.
+package slicest
+
+import "testing"
+
+func benchmarkFlattenInput(groups, groupSize int) [][]int {
+	in := make([][]int, groups)
+	for i := 0; i < groups; i++ {
+		row := make([]int, groupSize)
+		for j := 0; j < groupSize; j++ {
+			row[j] = i*groupSize + j
+		}
+		in[i] = row
+	}
+	return in
+}
+
+func BenchmarkFlatten(b *testing.B) {
+	cases := []struct {
+		name      string
+		groups    int
+		groupSize int
+	}{
+		{name: "small", groups: 8, groupSize: 8},
+		{name: "medium", groups: 64, groupSize: 16},
+		{name: "large", groups: 256, groupSize: 32},
+	}
+
+	for _, tc := range cases {
+		b.Run(tc.name, func(b *testing.B) {
+			input := benchmarkFlattenInput(tc.groups, tc.groupSize)
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				_ = Flatten(input)
+			}
+		})
+	}
+}
+
+func BenchmarkFlatten2(b *testing.B) {
+	cases := []struct {
+		name      string
+		groups    int
+		groupSize int
+	}{
+		{name: "small", groups: 8, groupSize: 8},
+		{name: "medium", groups: 64, groupSize: 16},
+		{name: "large", groups: 256, groupSize: 32},
+	}
+
+	for _, tc := range cases {
+		b.Run(tc.name, func(b *testing.B) {
+			input := benchmarkFlattenInput(tc.groups, tc.groupSize)
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				_ = Flatten2(input)
+			}
+		})
+	}
+}