Clients can now subscribe to specific resources and receive targeted
notifications when those resources change. Previously, calling
`notifyResourceUpdated` on the server would broadcast the notification
to every connected client regardless of interest — now only sessions
that have explicitly subscribed to a given resource URI receive the
update, making resource change propagation both correct and efficient.
The subscription lifecycle is fully handled: clients can subscribe and
unsubscribe at any time, and the server cleans up subscription state
when a session closes.
Supersedes #838.
Resolves#837, #776.
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Signed-off-by: Dariusz Jędrzejczyk <dariusz.jedrzejczyk@broadcom.com>