支付系统核心：配额限制与用户付费状态管理

- 添加 tokio 依赖用于异步测试
- 启用 User 结构体，添加 is_paid/is_admin/paid_expires_at 字段
- 添加 UpdatePaymentRequest 请求体
- insert_weather_data 集成配额检查逻辑
- 新增 get_user_by_id、count_user_weather_data、update_user_payment_status
- 添加 payment_fields 数据库迁移脚本

src/models.rs

@@ -272,8 +272,7 @@ pub struct WeatherData {
     pub wind_speed_suitability: String,
 }
 
-/*
-#[derive(Debug, Serialize, FromRow)]
+#[derive(Debug, Serialize, Deserialize, FromRow)]
 pub struct User {
     pub id: i32,
     #[serde(rename = "name")]
@@ -289,5 +288,17 @@ pub struct User {
     #[serde(rename = "desc")]
     #[sqlx(rename = "desc")]
     pub description: Option<String>,
+    #[sqlx(rename = "is_paid")]
+    pub is_paid: bool,
+    #[sqlx(rename = "is_admin")]
+    pub is_admin: bool,
+    #[sqlx(rename = "paid_expires_at")]
+    pub paid_expires_at: Option<chrono::DateTime<chrono::Utc>>,
+}
+
+// 管理员更新用户付费状态的请求体
+#[derive(Debug, Deserialize)]
+pub struct UpdatePaymentRequest {
+    pub is_paid: bool,
+    pub paid_expires_at: Option<String>, // ISO 8601 格式
 }
-*/