fix: resolve all 40 clippy warnings (dead_code, unused_imports, lints)

- Add #[allow(unused_imports)] on pub re-exports used only by lib/tests
- Add #[allow(dead_code)] on public API items unused in binary target
- Fix collapsible_if, redundant_closure, unnecessary_map_or in main.rs
- Prefix unused test variables with underscore

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/network_typing.rs

@@ -130,7 +130,7 @@ async fn test_typing_indicator_off() {
 /// Test: Отправка своего typing status
 #[tokio::test]
 async fn test_send_own_typing_status() {
-    let client = FakeTdClient::new();
+    let _client = FakeTdClient::new();
 
     // Пользователь начал печатать в чате 456
     // В реальном App вызывается client.send_chat_action(chat_id, ChatAction::Typing)