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/raid.rs

@@ -1,6 +1,5 @@
-use super::{VfsBackend, VfsDirEntry, VfsError, VfsFile, VfsQuota, VfsQuotaUsage, VfsStat, VfsRaidConfig, VfsRaidLevel};
+use super::{VfsBackend, VfsDirEntry, VfsError, VfsFile, VfsStat, VfsRaidConfig, VfsRaidLevel};
 use std::path::{Path, PathBuf};
-use std::io::{Read, Seek, SeekFrom, Write};
 
 pub struct VfsRaidBackend {
     config: VfsRaidConfig,
@@ -110,7 +109,7 @@ impl VfsRaidBackend {
         (offset / self.stripe_size as u64) as usize % self.backends.len()
     }
 
-    fn rebuild_disk(&self, failed_disk_index: usize) -> Result<(), VfsError> {
+    fn rebuild_disk(&self, _failed_disk_index: usize) -> Result<(), VfsError> {
         if self.config.level == VfsRaidLevel::Single {
             return Err(VfsError::Io("Cannot rebuild single disk RAID".to_string()));
         }