Is your feature request related to a problem or challenge? Please describe what you are trying to do.

GenericColumnWriter currently contains Box<dyn PageWriter>, as PageWriter lacks a Send bound this in turn makes ColumnWriter not send. This interferes with the use of column writer in multi-threaded code.

Describe the solution you'd like

I would like GenericColumnWriter: Send

Describe alternatives you've considered

Additional context
Found as part of #4280