Handle sorted vs unsorted inputs about zed

[henridf]

For future reference, @nwt added some ideas about the implementation of sortedness analysis here: #869 (comment)

[alfred-landrum]

The analysis mentioned above will likely happen in the query planner, though I don't know if it will happen in this initial epic for it: #1004

[mccanne]

Closing this since we decided zq doesn't try to take advantage of sorted data in any way and such optimization will all be handled at scale in the lake. Instead, zq just processes the values in order of the files.