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/cli/interface/webdav.rs

@@ -91,7 +91,7 @@ async fn run_webdav_server(
             });
 
         let valid = auth.is_some_and(|(u, p)| {
-            u == expected.username && expected.password.as_ref().map_or(true, |exp| p == *exp)
+            u == expected.username && expected.password.as_ref().is_none_or(|exp| p == *exp)
         });
 
         if !valid {