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/tooling_snapshot_printer.md

@@ -0,0 +1,13 @@
+# Tooling: MIR snapshot expansion & printer stabilization
+
+Summary:
+- MirPrinter の出力順/表記を安定させ、スナップショットテストを拡張。
+
+Scope/Tasks:
+- [ ] MirPrinter の順序・表記の固定化（deterministic）
+- [ ] tests/mir_snapshots/ を追加整備（loop/try/arith/compare/concat など）
+- [ ] スナップショット差分で後退検知できるよう整備
+
+Acceptance Criteria:
+- 代表ケースのスナップショットが緑で安定
+