Phase 10.10: GC Switchable Runtime & Unified Debug System 実装完了

Phase 10.10の主要実装:
- GcConfigBox: GC設定の実行時制御（counting/trace/barrier_strict）
- DebugConfigBox: デバッグ設定の統一管理（JIT events/stats/dump/dot）
- メソッドディスパッチ: system_methods.rsで両Boxのメソッド実装
- CountingGC動作確認: write_barriers正常カウント（VM実行時）

技術的詳細:
- BoxCore/BoxBase統一アーキテクチャを活用
- setFlag/getFlag/apply/summaryメソッドで統一API提供
- 環境変数経由でVM/JITランタイムと連携
- GcConfigBox.apply()は次回実行から有効（ランタイム作成前に環境変数参照）

テスト済み:
- examples/gc_counting_demo.nyash: CountingGCの動作確認
- write_barriers=3でArray.push/set, Map.setを正しくカウント
- NYASH_GC_TRACE=1でGC統計出力確認

Box-First哲学の体現: 設定も制御も観測もすべてBox！

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

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

src/boxes/gc_config_box.rs

@@ -0,0 +1,62 @@
+use crate::box_trait::{NyashBox, StringBox, BoolBox, VoidBox, BoxCore, BoxBase};
+use std::any::Any;
+
+#[derive(Debug, Clone)]
+pub struct GcConfigBox { base: BoxBase, counting: bool, trace: bool, barrier_strict: bool }
+
+impl GcConfigBox {
+    pub fn new() -> Self {
+        Self {
+            base: BoxBase::new(),
+            counting: std::env::var("NYASH_GC_COUNTING").ok().as_deref() == Some("1"),
+            trace: std::env::var("NYASH_GC_TRACE").ok().as_deref() == Some("1"),
+            barrier_strict: std::env::var("NYASH_GC_BARRIER_STRICT").ok().as_deref() == Some("1"),
+        }
+    }
+    pub fn set_flag(&mut self, name: &str, on: bool) -> Box<dyn NyashBox> {
+        match name {
+            "counting" => self.counting = on,
+            "trace" => self.trace = on,
+            "barrier_strict" | "strict" => self.barrier_strict = on,
+            _ => return Box::new(StringBox::new(format!("Unknown flag: {}", name)))
+        }
+        Box::new(VoidBox::new())
+    }
+    pub fn get_flag(&self, name: &str) -> Box<dyn NyashBox> {
+        let v = match name {
+            "counting" => self.counting,
+            "trace" => self.trace,
+            "barrier_strict" | "strict" => self.barrier_strict,
+            _ => false,
+        };
+        Box::new(BoolBox::new(v))
+    }
+    pub fn apply(&self) -> Box<dyn NyashBox> {
+        let setb = |k: &str, v: bool| { if v { std::env::set_var(k, "1"); } else { std::env::remove_var(k); } };
+        setb("NYASH_GC_COUNTING", self.counting);
+        setb("NYASH_GC_TRACE", self.trace);
+        setb("NYASH_GC_BARRIER_STRICT", self.barrier_strict);
+        Box::new(VoidBox::new())
+    }
+    pub fn summary(&self) -> Box<dyn NyashBox> {
+        let s = format!("counting={} trace={} barrier_strict={}", self.counting, self.trace, self.barrier_strict);
+        Box::new(StringBox::new(s))
+    }
+}
+
+impl BoxCore for GcConfigBox {
+    fn box_id(&self) -> u64 { self.base.id }
+    fn parent_type_id(&self) -> Option<std::any::TypeId> { self.base.parent_type_id }
+    fn fmt_box(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { write!(f, "GcConfigBox") }
+    fn as_any(&self) -> &dyn Any { self }
+    fn as_any_mut(&mut self) -> &mut dyn Any { self }
+}
+
+impl NyashBox for GcConfigBox {
+    fn equals(&self, other: &dyn NyashBox) -> BoolBox { BoolBox::new(other.as_any().is::<GcConfigBox>()) }
+    fn type_name(&self) -> &'static str { "GcConfigBox" }
+    fn clone_box(&self) -> Box<dyn NyashBox> { Box::new(self.clone()) }
+    fn share_box(&self) -> Box<dyn NyashBox> { self.clone_box() }
+    fn to_string_box(&self) -> StringBox { StringBox::new(self.summary().to_string_box().value) }
+}
+