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>

src/tdlib/mod.rs

@@ -17,6 +17,7 @@ pub mod users;
 pub use auth::AuthState;
 pub use client::TdClient;
 pub use r#trait::TdClientTrait;
+#[allow(unused_imports)]
 pub use types::{
     ChatInfo, FolderInfo, MediaInfo, MessageBuilder, MessageInfo, NetworkState, PhotoDownloadState,
     PhotoInfo, PlaybackState, PlaybackStatus, ProfileInfo, ReplyInfo, UserOnlineStatus,