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/webdav_version.rs

@@ -139,7 +139,7 @@ impl WebDavVersioning {
         let db = recover_rwlock(self.db.read());
         for (key, value) in db.iter() {
             if key.starts_with(&prefix) {
-                let version_info: VersionInfo = serde_json::from_slice(&value)?;
+                let version_info: VersionInfo = serde_json::from_slice(value)?;
                 versions.push(version_info);
             }
         }