[vvoytovych]

A presence that no hub binding declares heard its Network's deletion only at its next resync, up to a minute later (the wait): staging's kept-interface test measured 65 s (#829). The replicator mirrors every Network onto the hub (the mirror) and deletes the mirror as soon as the Network is deleted (its delete). The presence controller now watches those mirrors and maps a mirror's deletion to the hub copies of the network's contexts in the same namespace, as it maps an interface copy to its presence; the resync stays for an event that never arrives.

Built on #844, the restart fix, now on main: the map reads the hub's context copies from the informer #844 added.

Changes

change	file
The presence controller watches Networks on the hub. A mirror's deletion, or the first update of a deletion a finalizer holds, maps to the hub copies of the network's contexts in its namespace	networkpresence_controller.go

Corner cases

case	what happens	proof
A presence in its grace, its Network deleted	Marked and ended within seconds, with the resync set to an hour	TestANetworkDeletionReachesAPresenceNothingDeclaresAtOnce
A network in two locations	Both presences come back	TestANetworkMirrorMapsToItsPresencesInItsNamespace
Another network in the namespace, or the same name in another project	Not brought back	the same test
A mirror's creation, which every start lists, or its edit	Brings nothing back	TestOnlyANetworkMirrorGoingBringsItsPresencesBack
A mirror whose deletion a finalizer holds	Its first update counts	the same test
A mirror deleted while its Network lives	The presence reads the Network, which is not being deleted, and marks nothing	TestNetworkPresenceMarksOnlyTheContextOfTheNetworkBeingDeleted and the reconcile's own read
The mirror's deletion arrives before the project's cache shows the Network deleting	The presence waits, and its resync marks it	named, not tested

Cost

• One informer of Networks on the hub, one object per network. The replicator already watches them there, with the same identity, so no permission is new; the marker records it.
• On a deletion, one cached list of the namespace's context copies.

Test plan

• On the restart fix's branch the deletion test fails, with the resync at an hour, and it passes with the change.
• A planted defect per case turns its test red, 7 of 7, and golangci-lint v2.15.0 passes.
• On kind, with the NSO manager restarted and its new pod running the presence controller, a presence held past its grace was marked 0.3 s after its Network's deletion, 3 of 3, and the Network went about 3 s after it. Without this change it was marked at the next resync, 37 s and 60 s after.
• On staging, after the merge, kept_test.py's undeclared network went 4 s after its delete, where it took 65 s on fix: Name a cell's network contexts from the location it serves #833's build.

Closes #829