repair: row_level: unstall to_repair_rows_on_wire() destroying its input

to_repair_rows_on_wire() moves the contents of its input std::list
and is careful to yield after each element, but the final destruction
of the input list still deals with all of the list elements without
yielding. This is expensive as not all contents of repair_row are moved
(_dk_with_hash is of type lw_shared_ptr<const decorated_key_with_hash>).

To fix, destroy each row element as we move along. This is safe as we
own the input and don't reference row_list other than for the iteration.

Fixes #24725.

Closes scylladb/scylladb#24726

repair/row_level.cc

@@ -1448,7 +1448,9 @@ private:
         size_t row_bytes = co_await get_repair_rows_size(row_list);
         _metrics.tx_row_nr += row_list.size();
         _metrics.tx_row_bytes += row_bytes;
-        for (repair_row& r : row_list) {
+        while (!row_list.empty()) {
+            repair_row r = std::move(row_list.front());
+            row_list.pop_front();
             const auto& dk_with_hash = r.get_dk_with_hash();
             // No need to search from the beginning of the rows. Look at the end of repair_rows_on_wire is enough.
             if (rows.empty()) {