Add regression test for deltasync timestamp validation.
Add regression test for deltasync timestamp validation.

nylas/sync-engine,closeio/nylas,gale320/sync-engine,jobscore/sync-engine,closeio/nylas,ErinCall/sync-engine,wakermahmud/sync-engine,ErinCall/sync-engine,Eagles2F/sync-engine,closeio/nylas,jobscore/sync-engine,Eagles2F/sync-engine,gale320/sync-engine,jobscore/sync-engine,jobscore/sync-engine,Eagles2F/sync-engine,wakermahmud/sync-engine,closeio/nylas,nylas/sync-engine,Eagles2F/sync-engine,wakermahmud/sync-engine,gale320/sync-engine,Eagles2F/sync-engine,ErinCall/sync-engine,wakermahmud/sync-engine,ErinCall/sync-engine,wakermahmud/sync-engine,nylas/sync-engine,gale320/sync-engine,gale320/sync-engine,nylas/sync-engine,ErinCall/sync-engine