feat(gateway): 添加订单号缓存处理

- 在 ScanController 中集成 bigcache 用于缓存订单号
- 在处理扫码请求时，先检查订单号是否已存在缓存中
- 如果订单号已缓存，返回错误提示"订单已经提交~"
- 新增测试文件 scan_controller_test.go 用于验证缓存功能

go.sum

@@ -1,5 +1,7 @@
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 filippo.io/edwards25519 v1.1.0/go.mod h1:BxyFTGdWcka3PhytdK4V28tE5sGfRvvvRV7EaN4VDT4=
+github.com/allegro/bigcache/v3 v3.1.0 h1:H2Vp8VOvxcrB91o86fUSVJFqeuz8kpyyB02eH3bSzwk=
+github.com/allegro/bigcache/v3 v3.1.0/go.mod h1:aPyh7jEvrog9zAwx5N7+JUQX5dZTSGpxF1LAR4dr35I=
 github.com/beego/beego/v2 v2.3.4 h1:HurQEOGIEhLlPFCTR6ZDuQkybrUl2Ag2i6CdVD2rGiI=
 github.com/beego/beego/v2 v2.3.4/go.mod h1:5cqHsOHJIxkq44tBpRvtDe59GuVRVv/9/tyVDxd5ce4=
 github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=