修复 UR#55 代码审查问题：事务隔离、错误包装、重复辅助函数

- resolvePackageTerms 接受 tx 参数并使用事务绑定的 Store，确保快照与写入同库
- auto_purchase.go 错误包装改用 pkgerrors.Wrap 而非标准库 errors
- shop_package_batch_allocation 去除 fmt 依赖改用 strconv 拼接
- shop_series_grant 提取 effectiveBase 局部变量避免重复调用
- 测试辅助函数统一迁移至 testutil.StringPointer，删除各文件本地重复定义
- 新增 testutil.NewRedisClient 和 testutil.StringPointer

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/service/shop_series_grant/service.go

@@ -185,6 +185,7 @@ func (s *Service) buildGrantResponse(ctx context.Context, allocation *model.Shop
 		if pkg.IsGift {
 			continue
 		}
+		effectiveBase := packagepkg.EffectiveExpiryBase(pkg, pa)
 		packages = append(packages, dto.ShopSeriesGrantPackageItem{
 			PackageID:               pa.PackageID,
 			PackageName:             pkg.PackageName,
@@ -196,8 +197,8 @@ func (s *Service) buildGrantResponse(ctx context.Context, allocation *model.Shop
 			DefaultExpiryBaseName:   packagepkg.ExpiryBaseName(pkg.ExpiryBase),
 			ExpiryBaseOverride:      pa.ExpiryBaseOverride,
 			ExpiryBaseOverrideName:  packagepkg.ExpiryBaseOverrideName(pa.ExpiryBaseOverride),
-			EffectiveExpiryBase:     packagepkg.EffectiveExpiryBase(pkg, pa),
-			EffectiveExpiryBaseName: packagepkg.ExpiryBaseName(packagepkg.EffectiveExpiryBase(pkg, pa)),
+			EffectiveExpiryBase:     effectiveBase,
+			EffectiveExpiryBaseName: packagepkg.ExpiryBaseName(effectiveBase),
 		})
 	}
 	resp.Packages = packages