feat: init project with distributed lock implementation

- Add DistributedLock with Acquire/Release/Refresh using Lua scripts
- Add AcquireWithRetry with configurable retry interval and max retries
- Add integration tests for all lock operations
- Add .env for Redis connection (gitignored)

main.go

@@ -0,0 +1,60 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"os"
+	"time"
+
+	"github.com/joho/godotenv"
+	"github.com/redis/go-redis/v9"
+	"redis-rate-limiter/lock"
+)
+
+func main() {
+	// 加载 .env
+	if err := godotenv.Load(); err != nil {
+		log.Fatal("Error loading .env file")
+	}
+
+	// 连接 Redis
+	opt, err := redis.ParseURL(os.Getenv("REDIS_URL"))
+	if err != nil {
+		log.Fatalf("Invalid REDIS_URL: %v", err)
+	}
+
+	client := redis.NewClient(opt)
+	defer client.Close()
+
+	ctx := context.Background()
+
+	// 测试连接
+	if err := client.Ping(ctx).Err(); err != nil {
+		log.Fatalf("Redis connection failed: %v", err)
+	}
+	fmt.Println("✅ Redis connected")
+
+	// 示例：使用分布式锁
+	owner := fmt.Sprintf("instance-%d", time.Now().UnixNano())
+	l := lock.New(client, "my-resource-lock", owner, 10*time.Second)
+
+	// 尝试获取锁
+	acquired, err := l.Acquire(ctx)
+	if err != nil {
+		log.Fatalf("Acquire error: %v", err)
+	}
+	fmt.Printf("Lock acquired: %v\n", acquired)
+
+	if acquired {
+		// 模拟业务处理
+		fmt.Println("🔒 Holding lock, doing work...")
+		time.Sleep(2 * time.Second)
+
+		// 释放锁
+		if err := l.Release(ctx); err != nil {
+			log.Fatalf("Release error: %v", err)
+		}
+		fmt.Println("🔓 Lock released")
+	}
+}