Enable with_size_stream serialization

Enable with_size_stream serialization format for the String data type by default. This change is backward compatible, but the new serialization format is supported only since version 25.10, which means that downgrading to versions before 25.10 will not be possible. If you want to keep the possibility of downgrading to 25.9 and earlier, configure serialization_info_version as basic and string_serialization_version as single_stream in the merge_tree section of the server configuration. #89329 (Alexey Milovidov).