LocaleChangeNotifier
Signals that the OS locale or its regional preferences changed, so anything holding a formatted value can re-read it.
A ViewModel outlives the configuration change a locale switch triggers, so it never re-runs its initializers and a snapshot taken at construction goes stale — the user flips their temperature preference and the node list keeps showing Fahrenheit until the screen is rebuilt. Consumers therefore derive units from this flow rather than reading them once.
Emits only on change; collectors that need a current value start with their own read.