Add testListenValueEdit to DhtRunnerTester: verifies that editing
a value triggers an add callback (not an expire+add), and that
the edited value eventually expires.
Add testListenValueEdit and testPushListenValueEdit to
DhtProxyTester: same semantics tested over the long-poll and push
notification proxy paths.
Fix proxy tearDown order to destroy DhtProxyServer before shutting
down the proxy DhtRunner, preventing use-after-free on cancel.
Add unit tests for OpValueCache and ValueCache in isolation.
OpCacheTester covers add/edit/expire flows, refcount management,
and value synchronization lifecycle.
ValueCacheTester covers edition handling and value expiration.
Adrien Béraud