Optimize output writer

[CaptainCodeman]

Existing rolled-up files can be skipped, single file rollups can be done as a move (or copy/delete) and rollup needs to handle the number of source files being over the cloud storage rollup limit (i.e. perform iterative rollup).

[CaptainCodeman]

Rollup of > 32 files is now supported.

Need to detect or handle rollup where the total number of segments is > 1024 by re-writing the file(s) into a new one.