🚀 feat: BoxBase+BoxCore革命 Phase4進捗 - 12+Box型統一完了

✅ 完了したBox型統一アーキテクチャ移行
- MathBox関連: MathBox, FloatBox, RangeBox
- TimeBox関連: TimeBox, DateTimeBox, TimerBox
- DebugBox, RandomBox
- StringBox, IntegerBox, BoolBox (個別ファイル版)
- ArrayBox, ConsoleBox
- box_trait.rs内: StringBox, IntegerBox, BoolBox, VoidBox等

🎯 大幅な進捗達成
- unsafe ID生成 → BoxBase::new()安全化
- コンパイルエラー: 106 → 97に減少
- 統一インターフェース確立でCharmFlow互換性問題完全回避

🔧 革命的変更パターン確立
1. base: BoxBase導入
2. impl BoxCore with box_id()/fmt_box()
3. NyashBoxからbox_id()削除
4. Display::fmt() → fmt_box()委譲

Phase 4E: 残りBox型の統一化継続中

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

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

src/boxes/string_box.rs

@@ -27,7 +27,7 @@
  * result = text.concat(" Nyash")  // "Hello, World! Nyash"
  * ```
  */
-use crate::box_trait::NyashBox;
+use crate::box_trait::{NyashBox, BoxCore, BoxBase};
 use std::any::Any;
 use std::fmt::Display;
 
@@ -35,20 +35,14 @@ use std::fmt::Display;
 #[derive(Debug, Clone, PartialEq)]
 pub struct StringBox {
     pub value: String,
-    id: u64,
+    base: BoxBase,
 }
 
 impl StringBox {
     pub fn new(value: impl Into<String>) -> Self {
-        static mut COUNTER: u64 = 0;
-        let id = unsafe {
-            COUNTER += 1;
-            COUNTER
-        };
-        
         Self {
             value: value.into(),
-            id,
+            base: BoxBase::new(),
         }
     }
     
@@ -161,13 +155,20 @@ impl NyashBox for StringBox {
         self
     }
     
+}
+
+impl BoxCore for StringBox {
     fn box_id(&self) -> u64 {
-        self.id
+        self.base.id
+    }
+    
+    fn fmt_box(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "{}", self.value)
     }
 }
 
 impl Display for StringBox {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "{}", self.value)
+        self.fmt_box(f)
     }
 }