feat: Enhance plugin runtime with new component registry and workflow executor

- Introduced `ComponentRegistry` for managing plugin components with support for registration, enabling/disabling, and querying by type and plugin.
- Added `EventDispatcher` to handle event distribution to registered event handlers, supporting both blocking and non-blocking execution.
- Implemented `WorkflowExecutor` to manage a linear workflow execution across multiple stages, including command routing and error handling.
- Created `ManifestValidator` for validating plugin manifests against required fields and version compatibility.
- Updated `RPCClient` to use `MsgPackCodec` for message encoding.
- Enhanced `PluginRunner` to support lifecycle hooks for plugins, including `on_load` and `on_unload`.
- Added sys.path isolation to restrict plugin access to only necessary directories.

src/plugin_runtime/__init__.py

@@ -1,2 +1 @@
-# MaiBot Plugin Runtime - 插件隔离运行时基础设施
-# 本模块实现 Host-Runner 进程分离架构，提供 IPC 通信、策略引擎与生命周期管理
+