Verify at least one worker is selected in scheduleFixedNodeCount
Make ChannelSet immutable

Rewrite ChannelSet using GroupByHash as a template
Remove BlockCursor use in filter and project
Change aggregations to not use BlockCursor
Change GroupByHash to not use BlockCursor
Add appendTo method to Page
Change DistinctLimitOperator to not use BlockCursor
Change joins to no longer use BlockCursors
Change semi join to no longer use BlockCursors
Change MarkDistinctOperator to not use Cursors
Change PagesIndex to not use BlockCursors
Change SampleOpertor to no use BlockCursor
Change table writing operators to not use BlockCursors
Change TopNOperator to not use BlockCursors
Change LimitOperator to not use BlockCursors
Change MaterializeSampleOperator to not use BlockCursors
Change dictionary blocks to use GroupByHash
Change RunLengthEncoder to not use BlockCursors
Change uncompressed and snappy encoders to not use BlockCursors
Change MaterializedResult to not use BlockCursors