Implement SMB 3.x Lease support Phase 1-2

Phase 1: Open struct lease fields
- lease_key: Option<[u8; 16]> - LeaseKey GUID
- lease_state: Option<u32> - READ/HANDLE/WRITE flags
- lease_flags: Option<u32> - BREAKING etc.

Phase 2: LeaseManager
- LeaseEntry with lease_key/state/flags
- register/unregister/can_grant methods
- break_lease returns LeaseBreakNotification
- LeaseBreakNotification struct (MS-SMB2 §2.2.26)

ServerState: lease_manager field added

All 229 tests pass.

vendor/smb-server/src/server.rs

@@ -198,6 +198,8 @@ pub struct ServerState {
     pub shutting_down: Arc<AtomicBool>,
     /// Global oplock state manager (Phase 2).
     pub oplock_manager: Arc<crate::oplock::OplockManager>,
+    /// Global lease manager for SMB 3.x.
+    pub lease_manager: Arc<crate::oplock::LeaseManager>,
     /// Global byte-range lock manager (Phase 7).
     pub lock_manager: Arc<crate::oplock::LockManager>,
 }
@@ -213,6 +215,7 @@ impl ServerState {
             shutdown: Arc::new(Notify::new()),
             shutting_down: Arc::new(AtomicBool::new(false)),
             oplock_manager: Arc::new(crate::oplock::OplockManager::new()),
+            lease_manager: Arc::new(crate::oplock::LeaseManager::new()),
             lock_manager: Arc::new(crate::oplock::LockManager::new()),
         }
     }