Accept deadline in write args and callback for GC results

[meatballhat]

This introduces some considerable changes to the queue client GC so that the code using the method can take action in batches during the process. Every batch of keys considered "expired" is given to a callback function which may choose to return a specific error to interrupt iteration. The return signature of GC now returns (total, nDeleted, error) so that the code using it can report accordingly.

NOTE: This includes a backward-incompatible change to how "meta cancelation" entries are managed to use the bare "track value" rather than the SHA1 hex checksum of the "track value". This allows client usage to directly inspect the meta:cancelation hash with the "track value" understood by the client like so:

HGET meta:cancelation someInternalID9000

Part of RUNT-372 which addresses the problem of automatically + preemptively canceling work while it is still in the queue.

[NikhilSinha1]

Talked through this offline, still deciding on whether the callback function or returning a list of values is a better idea but otherwise this makes sense.

[NikhilSinha1]

Asked a bunch of questions over DM, LGTM