[combiner] remove array copy in transform one (#5432)
[combiner] remove array copy in transform one (#5432)

This passes the requireness issue upstream to the consumer of the
library. Add docs to explain this.
danking/hail,hail-is/hail,danking/hail,hail-is/hail,hail-is/hail,hail-is/hail,danking/hail,cseed/hail,cseed/hail,hail-is/hail,cseed/hail,cseed/hail,cseed/hail,danking/hail,cseed/hail,danking/hail,danking/hail,danking/hail,hail-is/hail,hail-is/hail,danking/hail,hail-is/hail,cseed/hail,cseed/hail