chore: remove dead code and unnecessary allow(dead_code) attributes

Cleaned up warnings by removing unused code:
- Removed unused format_timestamp() function from utils.rs
- Removed unused len() method from LruCache
- Removed unused date field from ForwardInfo struct
- Removed unnecessary #[allow(dead_code)] attributes from:
  * AuthState enum (actually used)
  * ChatInfo struct (actually used)
  * TdClient impl block (actually used)

This reduces code noise and makes real warnings more visible.

Changes:
- 20 lines removed
- 1 line added
- 6 files changed

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

src/utils.rs

@@ -52,12 +52,6 @@ fn parse_timezone_offset(tz: &str) -> i32 {
     3 // fallback к MSK
 }
 
-/// Устаревшая функция для обратной совместимости (используется дефолтный +03:00)
-#[allow(dead_code)]
-pub fn format_timestamp(timestamp: i32) -> String {
-    format_timestamp_with_tz(timestamp, "+03:00")
-}
-
 /// Форматирование timestamp в дату для разделителя
 pub fn format_date(timestamp: i32) -> String {
     use std::time::{SystemTime, UNIX_EPOCH};