feat(phase-9.75g-0): Complete BID-FFI Plugin System with enhanced plugin-tester

🎊 Phase 9.75g-0 COMPLETE - Revolutionary Plugin System Achievement\!

✅ Major Completions:
- plugin-tester type validation: nyash.toml integration & method signature verification
- Duplicate method name detection: Enforces Nyash no-overloading policy
- Comprehensive developer guide: 200+ line technical documentation
- Memory safety: HostVtable lifetime issues resolved with LazyLock
- Type information system: External nyash.toml configuration eliminates hardcoded conversions

🚀 Revolutionary Impact:
Nyash now supports dynamic Box type extension via plugins:
```nyash
local file = new FileBox()        // Plugin-provided
local db = new PostgreSQLBox()    // Future: Plugin-provided
local gpu = new CudaBox()         // Future: Plugin-provided
```

📊 Technical Achievements:
- plugin-tester: 4 comprehensive validation modes (check/lifecycle/io/typecheck)
- BID-FFI Protocol: Production-ready with valgrind-verified memory safety
- Type conversion: Automatic string→bytes mapping via nyash.toml
- Method validation: Prevents overloading conflicts in plugin development

🎯 Next Priority: Phase 8.6 VM Performance Improvement
Current issue: VM is 0.9x slower than interpreter (regression\!)
Target: 2x+ speedup for practical VM execution

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

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

test-nyash.toml

@@ -0,0 +1,29 @@
+# Test Configuration for plugin-tester
+# Valid TOML structure
+
+# Plugin name mappings (simple version)
+[plugin_names]
+FileBox = "nyash-filebox-plugin"
+
+# Plugin configurations with method type information
+[plugins.FileBox]
+plugin_name = "nyash-filebox-plugin"
+
+[plugins.FileBox.methods]
+# readは引数なし
+read = { args = [] }
+
+# writeは文字列をbytesとして送る
+write = { args = [{ from = "string", to = "bytes" }] }
+
+# openは2つの文字列引数
+open = { args = [
+    { name = "path", from = "string", to = "string" },
+    { name = "mode", from = "string", to = "string" }
+] }
+
+# closeは引数なし、戻り値なし
+close = { args = [] }
+
+# existsは引数なし、戻り値はbool（将来拡張）
+exists = { args = [], returns = "bool" }