refactor: cleanup unused code and warnings

Comprehensive cleanup of unused methods, dead code, and compiler warnings:

## Removed Methods (15):
- Duplicate delegation methods: is_authenticated, get_typing_text, get_user_name from TdClient
- Obsolete methods: TdClient::init() (duplicated in main.rs)
- Unused getters: UserCache::{get_username, get_name, get_user_id_by_chat}
- Unused builder methods: MessageBuilder::{edited, add_reaction}
- Unused utility: ChatState::is_normal()
- Dead code: HotkeysConfig::{matches, key_matches} (kept for tests)
- Unused method: UserCache::register_private_chat()
- Getter replaced with direct field access: MessageInfo::edit_date()

## Removed Module:
- error.rs - Unused error handling module (TeletuiError, ErrorVariant, IntoTeletuiError)

## Removed Constants (8):
- EMOJI_PICKER_COLUMNS, EMOJI_PICKER_ROWS, MAX_INPUT_HEIGHT
- MIN_TERMINAL_WIDTH, MIN_TERMINAL_HEIGHT
- TDLIB_CHAT_LIMIT, MAX_USERNAME_DISPLAY_LENGTH, MESSAGE_TEXT_INDENT

## Fixed Warnings:
- Removed unused imports (8 instances)
- Fixed unreachable patterns (10 instances)
- Fixed irrefutable if let patterns (2 instances)
- Fixed unused variables (1 instance)
- Removed dead_code annotations where appropriate

## Improvements:
- Integrated Config::load_credentials() into TdClient::new() for better credential management
- Replaced edit_date() getter with direct field access (message.metadata.edit_date)
- Updated tests to use direct field access instead of removed getters

## Test Results:
All tests passing: 499 passed, 0 failed

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/tdlib/users.rs

@@ -152,21 +152,6 @@ impl UserCache {
         }
     }
 
-    /// Получить username пользователя
-    pub fn get_username(&mut self, user_id: &UserId) -> Option<&String> {
-        self.user_usernames.get(user_id)
-    }
-
-    /// Получить имя пользователя
-    pub fn get_name(&mut self, user_id: &UserId) -> Option<&String> {
-        self.user_names.get(user_id)
-    }
-
-    /// Получить user_id по chat_id
-    pub fn get_user_id_by_chat(&self, chat_id: ChatId) -> Option<UserId> {
-        self.chat_user_ids.get(&chat_id).copied()
-    }
-
     /// Получить статус пользователя по chat_id
     pub fn get_status_by_chat_id(&self, chat_id: ChatId) -> Option<&UserOnlineStatus> {
         let user_id = self.chat_user_ids.get(&chat_id)?;
@@ -181,21 +166,20 @@ impl UserCache {
     ///
     /// * `user_enum` - Обновление пользователя от TDLib
     pub fn handle_user_update(&mut self, user_enum: &User) {
-        if let User::User(user) = user_enum {
-            let user_id = user.id;
+        let User::User(user) = user_enum;
+        let user_id = user.id;
 
-            // Сохраняем username
-            if let Some(username) = user.usernames.as_ref().map(|u| u.editable_username.clone()) {
-                self.user_usernames.insert(UserId::new(user_id), username);
-            }
-
-            // Сохраняем имя
-            let display_name = format!("{} {}", user.first_name, user.last_name).trim().to_string();
-            self.user_names.insert(UserId::new(user_id), display_name);
-
-            // Обновляем статус
-            self.update_status(UserId::new(user_id), &user.status);
+        // Сохраняем username
+        if let Some(username) = user.usernames.as_ref().map(|u| u.editable_username.clone()) {
+            self.user_usernames.insert(UserId::new(user_id), username);
         }
+
+        // Сохраняем имя
+        let display_name = format!("{} {}", user.first_name, user.last_name).trim().to_string();
+        self.user_names.insert(UserId::new(user_id), display_name);
+
+        // Обновляем статус
+        self.update_status(UserId::new(user_id), &user.status);
     }
 
     /// Обновляет онлайн-статус пользователя.
@@ -216,11 +200,6 @@ impl UserCache {
         self.user_statuses.insert(user_id, online_status);
     }
 
-    /// Сохранить связь chat_id -> user_id
-    pub fn register_private_chat(&mut self, chat_id: ChatId, user_id: UserId) {
-        self.chat_user_ids.insert(chat_id, user_id);
-    }
-
     /// Получает имя пользователя из кэша или загружает из TDLib.
     ///
     /// Сначала проверяет кэш, затем при необходимости загружает из API.