Port of Go server/reload.go option interface and diffing logic. Compares
NatsOptions property-by-property to detect changes, tags each with category
flags (logging, auth, TLS, non-reloadable), validates that non-reloadable
options (Host, Port, ServerName) are not changed at runtime, and provides
MergeCliOverrides to ensure CLI flags always take precedence over config
file values during hot reload.
