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/conn/state.rs

@@ -304,6 +304,10 @@ pub struct Open {
     // Oplock fields (MS-SMB2 §2.2.13 / §2.2.14)
     pub oplock_level: u8,
     pub share_access: u32,
+    // Lease fields (MS-SMB2 §2.2.13 for SMB 3.x)
+    pub lease_key: Option<[u8; 16]>,  // LeaseKey GUID
+    pub lease_state: Option<u32>,     // LeaseState (READ/HANDLE/WRITE)
+    pub lease_flags: Option<u32>,     // LeaseFlags (BREAKING etc.)
 }
 
 impl Open {
@@ -327,6 +331,9 @@ impl Open {
             search_state: None,
             oplock_level,
             share_access,
+            lease_key: None,
+            lease_state: None,
+            lease_flags: None,
         }
     }
 }