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/urls.rs

@@ -211,7 +211,7 @@ async fn dispatch_send(
                 "send for [key={}] failed, queued for retry in {delay_seconds:.1}s",
                 log_key(url)
             );
-            enqueue_retry(ctx.task_queue, task, delay_seconds).await;
+            enqueue_retry(ctx.task_queue, *task, delay_seconds).await;
             let _ = reply(
                 ctx.sender,
                 chat_id,