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/media/image_renderer.rs

@@ -108,6 +108,7 @@ impl ImageRenderer {
     }
 
     /// Удаляет протокол для сообщения
+    #[allow(dead_code)]
     pub fn remove(&mut self, msg_id: &MessageId) {
         let msg_id_i64 = msg_id.as_i64();
         self.protocols.remove(&msg_id_i64);
@@ -115,6 +116,7 @@ impl ImageRenderer {
     }
 
     /// Очищает все протоколы
+    #[allow(dead_code)]
     pub fn clear(&mut self) {
         self.protocols.clear();
         self.access_order.clear();