feat(mir): Phase 25.1f完了 - Conservative PHI + ControlForm観測レイヤー

🎉 Conservative PHI Box理論による完全SSA構築

**Phase 7-B: Conservative PHI実装**
- 片方branchのみ定義変数に対応（emit_void使用）
- 全変数にPHI生成（Conservative Box理論）
- Stage-1 resolver全テスト緑化（3/3 PASS）

**Phase 25.1f: ControlForm観測レイヤー**
- LoopShape/IfShape/ControlForm構造定義
- Loop/If統一インターフェース実装
- debug_dump/debug_validate機能追加
- NYASH_CONTROL_FORM_TRACE環境変数対応

**主な変更**:
- src/mir/builder/phi.rs: Conservative PHI実装
- src/mir/control_form.rs: ControlForm構造（NEW）
- src/mir/loop_builder.rs: LoopForm v2デフォルト化

**テスト結果**:
✅ mir_stage1_using_resolver_min_fragment_verifies
✅ mir_stage1_using_resolver_full_collect_entries_verifies
✅ mir_parserbox_parse_program2_harness_parses_minimal_source

🤖 Generated with Claude Code
Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: ChatGPT <chatgpt@openai.com>

src/mir/builder/call_resolution.rs

@@ -46,6 +46,7 @@ pub fn suggest_resolution(name: &str) -> String {
 
 /// Check if a method name is commonly shadowed by global functions
 /// Used for generating warnings about potential self-recursion
+#[allow(dead_code)]
 pub fn is_commonly_shadowed_method(method: &str) -> bool {
     matches!(
         method,
@@ -57,6 +58,7 @@ pub fn is_commonly_shadowed_method(method: &str) -> bool {
 }
 
 /// Generate warning message for potential self-recursion
+#[allow(dead_code)]
 pub fn generate_self_recursion_warning(box_name: &str, method: &str) -> String {
     format!(
         "Warning: Potential self-recursion detected in {}.{}(). \
@@ -102,4 +104,4 @@ mod tests {
         assert!(warning.contains("::print()"));
         assert!(warning.contains("self-recursion"));
     }
-}
+}