Wire up the config parsing infrastructure into the server:
- NatsServer: add ReloadConfig() with digest-based change detection,
diff/validate, CLI override preservation, and side-effect triggers
- Program.cs: two-pass CLI parsing — load config file first, then
apply CLI args on top with InCmdLine tracking for reload precedence
- SIGHUP handler upgraded from stub warning to actual reload
- Remove config file "not yet supported" warning from StartAsync
- Add integration tests for config loading, CLI overrides, and
reload validation
Replace empty catch blocks with meaningful log statements in NatsServer,
NatsClient, and Program. Add WaitForReadyAsync() to NatsServer for
deterministic server startup. Replace Task.Delay/Thread.Sleep in tests
with PING/PONG protocol flush and SubscribeCoreAsync for reliable
subscription synchronization.
