🔧 refactor: すべてのBoxをArc<Mutex>パターンで統一

CopilotのBox実装を私たちのArc<Mutex>パターンで統一：
- BufferBox: Arc<Mutex<Vec<u8>>>で内部可変性を実現
- FileBox: Arc<Mutex<File>>でファイルハンドル管理
- JSONBox: Arc<Mutex<Value>>でJSON値を保持
- HttpClientBox: Arc<Mutex<Client>>でHTTPクライアント管理
- StreamBox: Arc<Mutex>でストリームバッファと位置を管理
- RegexBox: Arc<Regex>で軽量ラッパー実装

各Boxに実用的なメソッドも追加：
- BufferBox: write, read, readAll, clear, length, append, slice
- FileBox: read, write, exists, delete, copy
- JSONBox: parse, stringify, get, set, has, keys
- HttpClientBox: get, post, put, delete, request
- StreamBox: write, read, position, length, reset
- RegexBox: test, find, findAll, replace, split

interpreterに新Box用のメソッド実行を追加：
- data_methods.rs: BufferBox, JSONBox, RegexBox
- network_methods.rs: HttpClientBox, StreamBox

これでコードベース全体が一貫性のあるArc<Mutex>パターンで統一されました！

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/interpreter/expressions.rs

@@ -8,6 +8,7 @@
 
 use super::*;
 use crate::ast::UnaryOperator;
+use crate::boxes::{BufferBox, JSONBox, HttpClientBox, StreamBox, RegexBox};
 // TODO: Fix NullBox import issue later
 // use crate::NullBox;
 
@@ -326,6 +327,11 @@ impl NyashInterpreter {
             return self.execute_array_method(array_box, method, arguments);
         }
         
+        // BufferBox method calls
+        if let Some(buffer_box) = obj_value.as_any().downcast_ref::<BufferBox>() {
+            return self.execute_buffer_method(buffer_box, method, arguments);
+        }
+        
         // FileBox method calls
         if let Some(file_box) = obj_value.as_any().downcast_ref::<FileBox>() {
             return self.execute_file_method(file_box, method, arguments);
@@ -346,6 +352,26 @@ impl NyashInterpreter {
             return self.execute_channel_method(channel_box, method, arguments);
         }
         
+        // JSONBox method calls
+        if let Some(json_box) = obj_value.as_any().downcast_ref::<JSONBox>() {
+            return self.execute_json_method(json_box, method, arguments);
+        }
+        
+        // HttpClientBox method calls
+        if let Some(http_box) = obj_value.as_any().downcast_ref::<HttpClientBox>() {
+            return self.execute_http_method(http_box, method, arguments);
+        }
+        
+        // StreamBox method calls
+        if let Some(stream_box) = obj_value.as_any().downcast_ref::<StreamBox>() {
+            return self.execute_stream_method(stream_box, method, arguments);
+        }
+        
+        // RegexBox method calls
+        if let Some(regex_box) = obj_value.as_any().downcast_ref::<RegexBox>() {
+            return self.execute_regex_method(regex_box, method, arguments);
+        }
+        
         // MathBox method calls
         if let Some(math_box) = obj_value.as_any().downcast_ref::<MathBox>() {
             return self.execute_math_method(math_box, method, arguments);