feat(v2): Order/Attempt/Account/Refund 模型 + 状态枚举 + :memory: 测试约定

v2 OrderStatus 三个值(Pending/Paid/Refunded)与 v1 model.OrderStatus 撞名,
统一加 V2 后缀(OrderPendingV2 等)规避包内重名;AttemptStatus/RefundStatus
无此冲突,原样保留。

internal/model/v2_test.go

@@ -0,0 +1,35 @@
+package model_test
+
+import (
+	"testing"
+
+	"github.com/wangjia/pay/internal/model"
+)
+
+func TestV2Migrate(t *testing.T) {
+	db := model.OpenTestDB(t)
+
+	o := model.OrderV2{
+		OutTradeNo: "PAY-1", MerchantID: 1, BizSystem: "pangolin", BizRef: "u-1",
+		ProductID: 3, Subject: "pro-year", AmountMinor: 29990000, Currency: "USDT",
+		Status: model.OrderPendingV2,
+	}
+	if err := db.Create(&o).Error; err != nil {
+		t.Fatalf("create order: %v", err)
+	}
+	a := model.Attempt{
+		OutTradeNo: "PAY-1", Channel: "crypto", AccountID: "usdt-a1", ProviderRef: "P-9",
+		RenderType: "crypto_address", AmountMinor: 29990000, Currency: "USDT",
+		Status: model.AttemptPending,
+	}
+	if err := db.Create(&a).Error; err != nil {
+		t.Fatalf("create attempt: %v", err)
+	}
+	var got model.OrderV2
+	if err := db.Where("out_trade_no = ?", "PAY-1").First(&got).Error; err != nil {
+		t.Fatalf("read: %v", err)
+	}
+	if got.AmountMinor != 29990000 || got.Status != model.OrderPendingV2 {
+		t.Fatalf("got %+v", got)
+	}
+}