DelayedPrinter
Run as usual with dotnet run, test as usual with dotnet test.
The delay algorithm is implemented using Redis' ZSET (sorted set) and a PUBSUB queue. When a print request arrives,
it's put to the scheduler's ZSET using requested print time (timestamp, resolution up to a second). The scheduler
checks this ZSET periodically, with a small random delay (to lower race conditions if there are multiple schedulers
running). When a message is ready to be printed, the scheduler immediately moves it to the print queue (PUBSUB) (the
move operation is executed under a lock, to eliminate race conditions between schedulers; the operation also wrapped in
a transaction, to not loose anything).