fix(v2): MarkAttemptPaid 按单scope+校验attempt命中 + OpenTestDB 唯一库名

- attempt UPDATE 加 out_trade_no 过滤并检查 RowsAffected,防止 order 已翻
  paid 但 providerRef 错配导致没有对应 attempt 被标记的账本背离(未命中
  时返回 error 触发事务回滚,order 保持 pending)
- 补测试覆盖 providerRef 错配场景:断言返回 error 且回滚后订单仍 pending
- OpenTestDB 改为每次调用生成唯一内存库名(atomic 计数器),避免同包多
  测试共享 file::memory:?cache=shared 导致数据串扰

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/model/testdb.go

@@ -1,6 +1,8 @@
 package model
 
 import (
+	"fmt"
+	"sync/atomic"
 	"testing"
 
 	"github.com/glebarez/sqlite"
@@ -8,11 +10,18 @@ import (
 	"gorm.io/gorm/logger"
 )
 
+var testDBCounter int64
+
 // OpenTestDB opens an in-memory SQLite DB with the v2 schema migrated.
 // Shared by all package tests (pay has no prior DB test harness — this is it).
+// Each call gets a uniquely named in-memory DB (cache=shared is still needed
+// so GORM's connection pool sees the same migrated schema across connections),
+// so concurrent/parallel tests in the same package don't share state.
 func OpenTestDB(t *testing.T) *gorm.DB {
 	t.Helper()
-	db, err := gorm.Open(sqlite.Open("file::memory:?cache=shared"),
+	n := atomic.AddInt64(&testDBCounter, 1)
+	dsn := fmt.Sprintf("file:testdb_%d?mode=memory&cache=shared", n)
+	db, err := gorm.Open(sqlite.Open(dsn),
 		&gorm.Config{Logger: logger.Default.LogMode(logger.Silent), TranslateError: true})
 	if err != nil {
 		t.Fatalf("open test db: %v", err)