Value::operator== ignores seq, so a node re-announcing identical content
with a bumped seq is the same value refreshed, not an edition. ValueCache
must not re-emit it: a source-counting OpValueCache above would count the
node twice and keep the value after the node is gone.
OpCacheTester and ValueCacheTester exercise the listen caches in
isolation: add/edit/expire flows, per-source refcounting, stale
versions, sync status, SearchCache::get and node drop.
DhtRunnerTester and DhtProxyTester gain end-to-end listen tests for
value edition, duplicate puts, multi-source and partial expiration,
get after a synced listen, and the push refresh/expire paths.
The proxy fixture joins the proxy DhtRunner before destroying the
DhtProxyServer so no DHT callback can reach a destroyed server, and
push notifications are never awaited while holding the mutex taken by
listen callbacks: the result is produced on the DHT thread.
Register the new executables in CMake and Meson.