Adds 8 new E2E tests to JetStreamTests.cs (tests 11-18) covering push
consumer config, AckNone/AckAll policies, Interest/WorkQueue retention,
ordered consumers, mirror streams, and source streams.
Fixes three server gaps exposed by the new tests: mirror JSON parsing
(deliver_subject and mirror object fields were silently ignored in stream
and consumer API handlers), and deliver_subject omitted from consumer
info wire format. Also fixes ShutdownDrainTests to use TaskCompletionSource
on ConnectionDisconnected instead of a Task.Delay poll loop.
5d9d1bebd5