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/server.rs

@@ -1,9 +1,8 @@
 use anyhow::Context;
 use axum::{
-    body::Body,
     extract::DefaultBodyLimit,
     extract::{Path, Query, State},
-    http::{HeaderMap, HeaderValue, StatusCode},
+    http::{HeaderMap, StatusCode},
     response::{Html, IntoResponse, Json},
     routing::{any, delete, get, patch, post, put},
     Extension,
@@ -12,7 +11,7 @@ use axum::{
 use base64::Engine as _;
 use serde::Deserialize;
 use std::str::FromStr;
-use std::sync::{Arc, LazyLock, Mutex, RwLock};
+use std::sync::{Arc, LazyLock, Mutex};
 use std::time::{Duration, Instant};
 
 use dashmap::DashMap;
@@ -2487,7 +2486,7 @@ struct CachedHandler {
 }
 
 static WEBDAV_HANDLER_CACHE: LazyLock<DashMap<String, CachedHandler>> =
-    LazyLock::new(|| DashMap::new());
+    LazyLock::new(DashMap::new);
 
 const WEBDAV_CACHE_TTL_SECS: u64 = 300; // 5 minutes