* fix(ecstore): retain namespace owners through local physical tails
(cherry picked from commit a2f242463316e87604feadbdac5e4148140e72c0)
* test(ecstore): expose stale fsync group cleanup
* fix(ecstore): capture complete fsync worker guard
(cherry picked from commit 1dc90bb836e20ea9ee45d0a629a9201e20d231c4)
* fix(ecstore): preserve successor fsync group registration
(cherry picked from commit c7dfaad90526052e56c57dafffa4813bdcde46ca)
* test(ecstore): mark physical owner fixtures as inline
* test(ecstore): wait for namespace owner release before asserting
The namespace owner tests decided that ownership had ended when the Weak probe stopped upgrading or when the mutation lease could be reacquired. Both signals fire before the owner guard's Drop decrements the pending counter: Arc releases its strong count before running Drop, and the lease drops its locks before its owner field. The rio-v2 lane hit that window in undo_fresh_version_keeps_physical_namespace_owner_after_timeout.
Extend every drain wait to also require namespace_commits_pending() to be false, so the assertions observe the completed release instead of racing it.
Zhengchao An