feat(plugin): Fix plugin BoxRef return and Box argument support

- Fixed deadlock in FileBox plugin copyFrom implementation (single lock)
- Added TLV Handle (tag=8) parsing in calls.rs for returned BoxRefs
- Improved plugin loader with config path consistency and detailed logging
- Fixed loader routing for proper Handle type_id/fini_method_id resolution
- Added detailed logging for TLV encoding/decoding in plugin_loader_v2

Test docs/examples/plugin_boxref_return.nyash now works correctly:
- cloneSelf() returns FileBox Handle properly
- copyFrom(Box) accepts plugin Box arguments
- Both FileBox instances close and fini correctly

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

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

docs/development/tools/vm_profiling_backend.md

@@ -0,0 +1,13 @@
+# VM: Micro-profiling & backend selection polish
+
+Summary:
+- VM 実行の簡易プロファイル（命令カウント/時間）と `--backend` の選択UI/エラー改善。
+
+Scope/Tasks:
+- [ ] VM: 命令実行回数/時間の簡易集計（ログ出力）
+- [ ] CLI: backend 未実装時のメッセージ改善（jit/wasm 選択時）
+- [ ] README: backend 選択例の追記
+
+Acceptance Criteria:
+- プロファイルログが出力され、選択ミス時のUI/メッセージが改善
+