feat: Add HTTP server/client E2E test for net plugin

- Implement full HTTP flow test: server → client → accept → respond → readBody
- All HTTP Box types working correctly (HttpServerBox, HttpClientBox, HttpRequestBox, HttpResponseBox)
- Handle type encoding for plugin method arguments working properly
- Test validates complete HTTP request/response cycle
- Net plugin E2E test passing ✅

HTTPネットワークプラグインのE2Eテスト追加
- サーバー起動からレスポンス読み取りまでの完全なフロー検証
- Handle型引数のTLVエンコーディングも正常動作
- 非同期HTTPフローの完全動作確認

🤖 Generated with Claude Code

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

plugins/nyash-net-plugin/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "nyash-net-plugin"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+crate-type = ["cdylib"]
+
+[dependencies]
+once_cell = "1.20"
+
+[features]
+default = []
+
+[profile.release]
+lto = true
+strip = true
+opt-level = "z"
+