Covers 6 implementation layers: ClientKind enum + INatsClient interface,
event infrastructure with Channel<T>, system event publishing, request-reply
monitoring services, import/export model with ACCOUNT client, and response
routing with latency tracking.
Adds LogOverrides property to NatsOptions and a --log_level_override=namespace=level CLI flag that wires Serilog MinimumLevel.Override entries so operators can tune verbosity per .NET namespace without changing the global log level.
Adds 10 new fields to NatsOptions (ClientAdvertise, TraceVerbose, MaxTracedMsgLen,
DisableSublistCache, ConnectErrorReports, ReconnectErrorReports, NoHeaderSupport,
MaxClosedClients, NoSystemAccount, SystemAccount) plus InCmdLine tracking set.
Moves MaxClosedClients from a private constant in NatsServer to a configurable option.
