roots StateFlow on session

[rnett]

Is your feature request related to a problem? Please describe.

I would like to be able to get the current server roots without needing to send a request to the client every time. This is supported by the roots changed notification.

Describe the solution you'd like

For the server session object to have a roots: MutableStateFlow<PersistentSet<String>> property or similar, that it updates based on received roots notifications. Ideally it would list the roots when first collected.

Describe alternatives you've considered
Always listing the roots, which works but adds a bunch of overhead.

Additional context
Add any other context or screenshots about the feature request here.