test: 补充单元测试覆盖率 29.9% → 36.6%

新建 18 个测试文件，追加 30 个已有测试文件，覆盖协议解析、
错误分类、CEL 表达式求值、YAML 反序列化、字节编码等纯函数。

plugins/services/redis_test.go

@@ -3,6 +3,7 @@
 package services
 
 import (
+	"errors"
 	"net"
 	"strings"
 	"testing"
@@ -32,3 +33,24 @@ func (c *redisReplyTestConn) RemoteAddr() net.Addr             { return nil }
 func (c *redisReplyTestConn) SetDeadline(time.Time) error      { return nil }
 func (c *redisReplyTestConn) SetReadDeadline(time.Time) error  { return nil }
 func (c *redisReplyTestConn) SetWriteDeadline(time.Time) error { return nil }
+
+func TestClassifyRedisErrorType(t *testing.T) {
+	tests := []struct {
+		name string
+		err  error
+		want ErrorType
+	}{
+		{"nil", nil, ErrorTypeUnknown},
+		{"wrongpass", errors.New("wrongpass invalid password"), ErrorTypeAuth},
+		{"noauth", errors.New("noauth authentication required"), ErrorTypeAuth},
+		{"connection refused", errors.New("connection refused"), ErrorTypeNetwork},
+		{"unknown", errors.New("random redis error"), ErrorTypeUnknown},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := classifyRedisErrorType(tt.err); got != tt.want {
+				t.Errorf("classifyRedisErrorType() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}