filer: cooling-off dual-read for POSIX locks during ring changes (#9672)

While the ring changed within the last snapshot interval, a fresh owner
asks the key's previous owner (LockRing.PriorOwner) whether it still
holds a conflicting lock before granting TRY_LOCK or answering GET_LK, so
it does not double-grant before re-assertion rebuilds its local state.
The probe is marked cooling_probe so the previous owner answers from
local state without recursing. PriorOwner uses the snapshot's prebuilt
ring rather than rebuilding a hash ring per call.

other/java/client/src/main/proto/filer.proto

@@ -388,6 +388,8 @@ message PosixLockRequest {
     bool is_moved = 2;
     PosixLockOp op = 3;
     PosixLockRange lock = 4;
+    repeated PosixLockRange locks = 5;
+    bool cooling_probe = 6;
 }
 
 enum PosixLockOp {