This series adds handling of null std::unique_ptr to utils::clear_gently and handling of std::optional and seastar::optimized_optional (both engaged and disengaged cases). Also, unit tests were added to tests the above cases. Fixes #13636 Closes #13638 * github.com:scylladb/scylladb: utils: clear_gently: add variants for optional values utils: clear_gently: do not clear null unique_ptr