Refactor protocol and transport modules to use type hints for improved clarity and consistency

- Updated Codec class to use abstract methods for encoding and decoding envelopes.
- Changed Envelope class to use Dict and Optional for payload and error fields.
- Refined error handling in RPCError class with Optional type hints for details.
- Enhanced manifest validation logic with type hints for better type safety.
- Improved plugin loading mechanism with consistent type annotations.
- Updated RPCClient to utilize Optional for codec and connection attributes.
- Refactored transport classes to use Optional for server attributes and socket paths.

src/plugin_runtime/transport/base.py

@@ -8,7 +8,7 @@
 """
 
 from abc import ABC, abstractmethod
-from typing import AsyncIterator, Callable, Awaitable
+from typing import Awaitable, Callable
 
 import asyncio
 import struct

src/plugin_runtime/transport/factory.py

@@ -3,12 +3,14 @@
 根据运行平台自动选择最优传输实现。
 """
 
+from typing import Optional
+
 import sys
 
 from .base import TransportClient, TransportServer
 
 
-def create_transport_server(socket_path: str | None = None) -> TransportServer:
+def create_transport_server(socket_path: Optional[str] = None) -> TransportServer:
     """创建传输服务端
 
     Linux/macOS 使用 UDS，Windows 使用 TCP 回退。

src/plugin_runtime/transport/tcp.py

@@ -4,6 +4,8 @@
 绑定到 127.0.0.1 避免远程访问，但仍需会话令牌做身份校验。
 """
 
+from typing import Optional
+
 import asyncio
 
 from .base import Connection, ConnectionHandler, TransportClient, TransportServer
@@ -20,7 +22,7 @@ class TCPTransportServer(TransportServer):
     def __init__(self, host: str = "127.0.0.1", port: int = 0):
         self._host = host
         self._port = port  # 0 表示自动分配
-        self._server: asyncio.AbstractServer | None = None
+        self._server: Optional[asyncio.AbstractServer] = None
         self._actual_port: int = 0
 
     async def start(self, handler: ConnectionHandler) -> None:

src/plugin_runtime/transport/uds.py

@@ -4,6 +4,7 @@
 """
 
 from pathlib import Path
+from typing import Optional
 
 import asyncio
 import os
@@ -20,13 +21,13 @@ class UDSConnection(Connection):
 class UDSTransportServer(TransportServer):
     """UDS 传输服务端"""
 
-    def __init__(self, socket_path: str | None = None):
+    def __init__(self, socket_path: Optional[str] = None):
         if socket_path is None:
             # 默认放在临时目录，使用 uuid 确保同一进程多实例不碰撞
             import uuid
             socket_path = os.path.join(tempfile.gettempdir(), f"maibot-plugin-{os.getpid()}-{uuid.uuid4().hex[:8]}.sock")
         self._socket_path = socket_path
-        self._server: asyncio.AbstractServer | None = None
+        self._server: Optional[asyncio.AbstractServer] = None
 
     async def start(self, handler: ConnectionHandler) -> None:
         # 清理残留 socket 文件