Release v19.86.0

Added

• Reactor and reducer deliveries carry a delivery id, which the .NET client returns with each result. Clients that do not return it keep working: their results complete the oldest outstanding delivery for the partition. (part of #4664)

Fixed

• A reactor or reducer result now completes only the delivery it answers. The kernel matched results by partition alone, so a late result for a timed-out delivery could complete the wait of that partition's retry, and completing one delivery could drop the next one for the same partition and leave it blocked until the client reconnected. A duplicate result no longer breaks the result stream. (part of #4664)