When handling `repair_stream_cmd::end_of_current_rows`, passing the
foreign list directly to `put_row_diff_handler` triggered a massive
synchronous deep copy on the destination shard. Additionally, destroying
the list triggered a synchronous deallocation on the source shard. This
blocked the reactor and triggered the CPU stall detector.
This commit fixes the issue by introducing `clone_gently()` to copy the
list elements one by one, and leveraging the existing
`utils::clear_gently()` to destroy them. Both utilize
`seastar::coroutine::maybe_yield()` to allow the reactor to breathe
during large cross-shard transfers and cleanups.
Fixes SCYLLADB-403
Closesscylladb/scylladb#28979
6cb263bab0