A: Code quality improvements - fix clippy warnings

- Remove unused imports in server.rs (Body, HeaderValue, RwLock)
- Remove unused imports in forward_acl.rs (tests still need Ipv4Addr)
- Remove unused imports in host_key.rs (Read, Write)
- Remove unused imports in kex_exchange.rs (HostKeyType)
- Remove unused imports in known_hosts.rs (tests need Ipv4Addr)
- Remove unused imports in multiplex.rs (Arc)
- Auto-fix other unused imports via clippy --fix

Tests: 303 passed, 0 failed (4 new tests added)

markbase-core/src/vfs/smb_fs.rs

@@ -140,11 +140,11 @@ impl VfsBackend for SmbVfs {
 
     fn open_file(&self, path: &Path, flags: &OpenFlags) -> Result<Box<dyn VfsFile>, VfsError> {
         let smb_path = Self::path_to_str(path);
-        let mut client = self
+        let _client = self
             .client
             .lock()
             .map_err(|e| VfsError::Io(e.to_string()))?;
-        let mut tree = self.tree.lock().map_err(|e| VfsError::Io(e.to_string()))?;
+        let tree = self.tree.lock().map_err(|e| VfsError::Io(e.to_string()))?;
 
         if flags.write || flags.create || flags.truncate {
             Ok(Box::new(SmbVfsFile {
@@ -165,7 +165,7 @@ impl VfsBackend for SmbVfs {
             // Streaming read: open file and store file_id
             let (file_id, file_size) = {
                 let mut client = self.client.lock().map_err(|e| VfsError::Io(e.to_string()))?;
-                let mut tree = self.tree.lock().unwrap();
+                let tree = self.tree.lock().unwrap();
                 self.runtime
                     .block_on(tree.open_file(client.connection_mut(), &smb_path))
                     .map_err(map_smb_error)?