Implement SMB Oplocks Phase 3+5

Phase 3: NotificationQueue
- Add notification_tx to Connection struct
- Modify writer.rs to use tokio::select! for response + notification
- Add write_to_bytes() to OplockBreakNotification
- Support server→client async messages

Phase 5: WRITE Handler oplock break
- Get path/share_access before write
- Trigger OplockManager.break_oplock()
- Send OPLOCK_BREAK_NOTIFICATION to affected clients
- Encode and send via notification channel

All 229 tests pass.

vendor/smb-server/src/conn/state.rs

@@ -8,7 +8,7 @@ use std::sync::{Arc, Mutex};
 use crate::proto::auth::ntlm::{Identity, NtlmServer};
 use crate::proto::crypto::{PreauthIntegrity, SigningAlgo};
 use crate::proto::messages::{Dialect, FileId};
-use tokio::sync::RwLock;
+use tokio::sync::{mpsc, RwLock};
 use uuid::Uuid;
 
 use crate::backend::Handle;
@@ -16,6 +16,9 @@ use crate::builder::Access;
 use crate::path::SmbPath;
 use crate::server::ShareBindings;
 
+/// Phase 3: Notification sender type for server→client async messages.
+pub type NotificationSender = mpsc::Sender<Vec<u8>>;
+
 /// In-flight NTLM acceptor + a `is_raw_ntlmssp` flag (true = raw, false =
 /// SPNEGO-wrapped). The handler hands the second-round response back in the
 /// same form the client opened with.
@@ -54,6 +57,9 @@ pub struct Connection {
 
     /// Monotonic SessionId allocator.
     next_session_id: AtomicU64,
+    
+    /// Phase 3: Notification sender for server→client async messages (oplock breaks).
+    pub notification_tx: RwLock<Option<NotificationSender>>,
 }
 
 impl Connection {
@@ -70,6 +76,7 @@ impl Connection {
             pending_auths: RwLock::new(HashMap::new()),
             session_preauth: RwLock::new(HashMap::new()),
             next_session_id: AtomicU64::new(1),
+            notification_tx: RwLock::new(None),
         }
     }