fix(phase-4.3c-3): Fix StringBox literal handling in MIR builder

Phase 4-3c-3 Complete: WASM host functions now correctly output string content

## Changes:
- Fixed MIR builder to handle StringBox with string literal arguments
- Special case for  to generate proper string constants
- Removed debug output after successful verification
- WASM now correctly outputs "Hello MIR!" instead of "StringBox"

## Test Results:
- MIR generation: ✅ Generates  correctly
- WASM compilation: ✅ String data correctly placed at offset 4096
- WASM execution: ✅ Outputs "Hello MIR\!" as expected

## Technical Details:
- Modified build_new_expression() to detect StringBox with literal arguments
- Generates Const instruction with actual string content
- Host function reads StringBox memory layout correctly

This completes the WASM string output functionality for Phase 4.

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

local_tests/perf_comparison.sh

@@ -0,0 +1,58 @@
+#!/bin/bash
+# FileBox パフォーマンス比較
+
+echo "🔬 FileBox 静的版 vs 動的版 パフォーマンス比較"
+echo "============================================="
+echo "テスト内容: 100個のファイル作成・書き込み・読み込み・存在確認"
+echo ""
+
+# クリーンアップ
+rm -f perf_test_*.txt
+
+# 動的版（現在）
+echo "1️⃣ 動的版 (dynamic-file feature 有効)"
+echo -n "   実行時間: "
+{ time RUST_LOG=error ./target/release/nyash local_tests/benchmark_filebox_simple.nyash > /dev/null 2>&1; } 2>&1 | grep real | awk '{print $2}'
+rm -f perf_test_*.txt
+
+# 静的版ビルド
+echo ""
+echo "   静的版をビルド中..."
+cargo build --release --no-default-features -j32 > /dev/null 2>&1
+
+# 静的版
+echo ""
+echo "2️⃣ 静的版 (FileBox組み込み)"
+echo -n "   実行時間: "
+{ time RUST_LOG=error ./target/release/nyash local_tests/benchmark_filebox_simple.nyash > /dev/null 2>&1; } 2>&1 | grep real | awk '{print $2}'
+rm -f perf_test_*.txt
+
+# 複数回測定
+echo ""
+echo "📊 5回測定の平均:"
+echo ""
+echo "動的版:"
+for i in {1..5}; do
+    echo -n "  Run $i: "
+    { time RUST_LOG=error ./target/release/nyash local_tests/benchmark_filebox_simple.nyash > /dev/null 2>&1; } 2>&1 | grep real | awk '{print $2}'
+    rm -f perf_test_*.txt
+done
+
+# 静的版に切り替え
+cargo build --release --no-default-features -j32 > /dev/null 2>&1
+
+echo ""
+echo "静的版:"
+for i in {1..5}; do
+    echo -n "  Run $i: "
+    { time RUST_LOG=error ./target/release/nyash local_tests/benchmark_filebox_simple.nyash > /dev/null 2>&1; } 2>&1 | grep real | awk '{print $2}'
+    rm -f perf_test_*.txt
+done
+
+# 動的版に戻す
+echo ""
+echo "元の動的版に戻しています..."
+cargo build --release -j32 > /dev/null 2>&1
+
+echo ""
+echo "✅ 測定完了！"