feat!: add telegram auth and async refactor

- Removed "/schedule/update-download-url" endpoint, this mechanism was replaced by Yandex Cloud FaaS. Ура :)
- Improved schedule caching mechanism.
- Added Telegram WebApp authentication support.
- Reworked endpoints responses and errors mechanism.
- Refactored application state management.
- Make synchronous database operations, middlewares and extractors to asynchronous.
- Made user password field optional to support multiple auth methods.
- Renamed users table column "version" to "android_version" and made it nullable.

src/database/models.rs

@@ -38,22 +38,25 @@ pub struct User {
     pub username: String,
 
     /// BCrypt password hash.
-    pub password: String,
+    pub password: Option<String>,
 
     /// ID of the linked VK account.
     pub vk_id: Option<i32>,
 
     /// JWT access token.
-    pub access_token: String,
+    pub access_token: Option<String>,
 
     /// Group.
-    pub group: String,
+    pub group: Option<String>,
 
     /// Role.
     pub role: UserRole,
 
     /// Version of the installed Polytechnic+ application.
-    pub version: String,
+    pub android_version: Option<String>,
+
+    /// ID of the linked Telegram account.
+    pub telegram_id: Option<i64>,
 }
 
 #[derive(