perf(loadbalance): add benchmarks for Least Time and Sticky

- Benchmark Select and Record operations
- Concurrent benchmark for realistic load testing
- Baseline performance:
  - LeastTime.Select: ~33ns/op, 0 allocs
  - LeastTime.Record: ~5.6ns/op, 0 allocs
  - StickySession.Select: ~205ns/op (with cookie lookup)

internal/loadbalance/least_time_bench_test.go

@@ -0,0 +1,96 @@
+package loadbalance
+
+import (
+	"testing"
+	"time"
+
+	"github.com/valyala/fasthttp"
+)
+
+func BenchmarkLeastTime_Select(b *testing.B) {
+	lt := NewLeastTime("last_byte", time.Millisecond)
+	targets := []*Target{
+		NewTargetFromConfig("http://a:8080", 1, 0, 0, 0, false, false, ""),
+		NewTargetFromConfig("http://b:8080", 1, 0, 0, 0, false, false, ""),
+		NewTargetFromConfig("http://c:8080", 1, 0, 0, 0, false, false, ""),
+	}
+
+	// Pre-populate stats
+	for _, t := range targets {
+		t.Stats.Record(10*time.Millisecond, 20*time.Millisecond)
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		lt.Select(targets)
+	}
+}
+
+func BenchmarkLeastTime_Record(b *testing.B) {
+	stats := NewEWMAStats()
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		stats.Record(10*time.Millisecond, 20*time.Millisecond)
+	}
+}
+
+func BenchmarkLeastTime_Concurrent(b *testing.B) {
+	lt := NewLeastTime("last_byte", time.Millisecond)
+	targets := []*Target{
+		NewTargetFromConfig("http://a:8080", 1, 0, 0, 0, false, false, ""),
+		NewTargetFromConfig("http://b:8080", 1, 0, 0, 0, false, false, ""),
+	}
+
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			lt.Select(targets)
+		}
+	})
+}
+
+func BenchmarkStickySession_Select(b *testing.B) {
+	fallback := NewRoundRobin()
+	config := DefaultStickyConfig()
+
+	sticky := NewStickySession(config, fallback)
+	sticky.Start()
+	defer sticky.Stop()
+
+	targets := []*Target{
+		NewTargetFromConfig("http://backend1:8080", 1, 0, 0, 0, false, false, ""),
+		NewTargetFromConfig("http://backend2:8080", 1, 0, 0, 0, false, false, ""),
+	}
+
+	// Pre-populate a cookie
+	ctx := &fasthttp.RequestCtx{}
+	sticky.Select(ctx, targets)
+	cookie := ctx.Response.Header.PeekCookie(config.Name)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		ctx := &fasthttp.RequestCtx{}
+		ctx.Request.Header.SetCookie(config.Name, string(extractCookieValue(cookie)))
+		sticky.Select(ctx, targets)
+	}
+}
+
+func BenchmarkStickySession_SelectNew(b *testing.B) {
+	fallback := NewRoundRobin()
+	config := DefaultStickyConfig()
+
+	sticky := NewStickySession(config, fallback)
+	sticky.Start()
+	defer sticky.Stop()
+
+	targets := []*Target{
+		NewTargetFromConfig("http://backend1:8080", 1, 0, 0, 0, false, false, ""),
+		NewTargetFromConfig("http://backend2:8080", 1, 0, 0, 0, false, false, ""),
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		ctx := &fasthttp.RequestCtx{}
+		sticky.Select(ctx, targets)
+	}
+}