fix(lint): resolve clippy warnings from rust 1.98

- photo.rs: chunks_exact(4)/(2) -> as_chunks::<N>().0
  (chunks_exact_to_as_chunks, the new lint prefers the
  compile-time-checked slice split)
- send.rs: box the Task inside SendError so the error fits the
  result_large_err limit (Task is ~400 bytes; the error now moves
  through Result as a pointer); unbox with *task at the two
  enqueue_retry call sites (handlers/urls.rs, handlers/callback.rs)

cargo clippy --workspace --all-targets is now warning-free; the
remaining proc-macro-error2 future-incompat note is upstream
(teloxide -> aquamarine) and unfixable locally. Full test suite passes.

crates/xmedia-bot/src/handlers/callback.rs

@@ -83,7 +83,7 @@ pub async fn callback_query_handler(bot: Bot, query: CallbackQuery) -> Result<()
                         task,
                     }) => {
                         log::info!("forward queued for retry in {delay_seconds:.1}s");
-                        enqueue_retry(&TASK_QUEUE, task, delay_seconds).await;
+                        enqueue_retry(&TASK_QUEUE, *task, delay_seconds).await;
                         bot.answer_callback_query(callback_query_id)
                             .text("Forward queued for retry.")
                             .await?;