feat(stat): 添加模型请求按天统计功能

- 新增统计控制器、服务层与数据访问层，提供按天统计接口
- 在 worker 处理任务时原子累加请求计数（仅实际调用模型时计数）
- 更新数据库表结构，添加 asynch_model_stat 表及索引
- 更新文档说明统计功能的使用方式与统计口径

service/stat_service.go

@@ -0,0 +1,40 @@
+package service
+
+import (
+	"context"
+
+	"model-asynch/dao"
+	"model-asynch/model/dto"
+)
+
+type statService struct{}
+
+var Stat = &statService{}
+
+func (s *statService) List(ctx context.Context, req *dto.ListModelStatReq) (res *dto.ListModelStatRes, err error) {
+	pageNum, pageSize := 1, 10
+	if req != nil && req.Page != nil {
+		if req.Page.PageNum > 0 {
+			pageNum = int(req.Page.PageNum)
+		}
+		if req.Page.PageSize > 0 {
+			pageSize = int(req.Page.PageSize)
+		}
+	}
+	startDay, endDay := "", ""
+	var tenantID *int64
+	creator, modelName := "", ""
+	if req != nil {
+		startDay = req.StartDay
+		endDay = req.EndDay
+		tenantID = req.TenantID
+		creator = req.Creator
+		modelName = req.ModelName
+	}
+	list, total, err := dao.Stat.List(ctx, pageNum, pageSize, startDay, endDay, tenantID, creator, modelName)
+	if err != nil {
+		return nil, err
+	}
+	return &dto.ListModelStatRes{List: list, Total: total}, nil
+}
+