refactor(server,middleware): 提取常量提高代码可读性

- ratelimit: 使用 accessUnknown 常量替代硬编码字符串
- testutil: 提取 testListenAddr 常量

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/middleware/security/ratelimit.go

@@ -339,7 +339,7 @@ func (rl *RateLimiter) getRetryAfter(key string) int64 {
 func keyByIP(ctx *fasthttp.RequestCtx) string {
 	ip := netutil.ExtractClientIPNet(ctx)
 	if ip == nil {
-		return "unknown"
+		return accessUnknown
 	}
 	return ip.String()
 }

internal/server/testutil.go

@@ -12,6 +12,9 @@ import (
 	"rua.plus/lolly/internal/ssl"
 )
 
+// testListenAddr 是测试用的随机端口监听地址
+const testListenAddr = "127.0.0.1:0"
+
 // MockFastServer 是 fasthttp.Server 的 Mock 包装
 // 定义在此文件以便 TestServerOptions 可以引用
 type MockFastServer struct {
@@ -108,7 +111,7 @@ func MustStartTestServer(cfg *config.Config) *Server {
 	}
 	if listenAddr == "" || listenAddr == ":80" {
 		if len(cfg.Servers) > 0 {
-			cfg.Servers[0].Listen = "127.0.0.1:0"
+			cfg.Servers[0].Listen = testListenAddr
 		}
 	}