Remove the memcpy for UnsafeRowOpt

Now we need to memcpy the entire row for UnsafeRowOpt because of usage of row header. It would be great to remove the memcpy for UnsafeRowOpt by not depending on row header in some cases.

Look at the UnsafeRowOpt implementation, likely in a file like core/row_opt.cpp or similar. Understand the current row header usage and memcpy. Identify cases where the header dependency can be avoided. Test changes with existing unit tests for row operations and performance benchmarks.

Written by the indexing model from the issue text.