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/s3_policy.rs

@@ -79,8 +79,8 @@ impl BucketPolicy {
         let mut allowed = false;
         
         for stmt in &self.statement {
-            if stmt.matches_action(action) && stmt.matches_resource(resource) {
-                if stmt.principal.matches_user(user_id) {
+            if stmt.matches_action(action) && stmt.matches_resource(resource)
+                && stmt.principal.matches_user(user_id) {
                     match stmt.effect {
                         PolicyEffect::Allow => {
                             if stmt.matches_condition(user_id) {
@@ -94,7 +94,6 @@ impl BucketPolicy {
                         }
                     }
                 }
-            }
         }
         
         allowed
@@ -120,11 +119,10 @@ impl PolicyStatement {
         if let Some(cond) = &self.condition {
             for (operator, values) in cond {
                 for (key, value) in values {
-                    if operator == "StringEquals" && key == "aws:userid" {
-                        if value != _user_id {
+                    if operator == "StringEquals" && key == "aws:userid"
+                        && value != _user_id {
                             return false;
                         }
-                    }
                 }
             }
         }