feat: Enhance legacy API with message chain support and new context handling

- Updated `LegacyContext.send_message` to handle rich message chains using `send_chain`.
- Introduced `LegacyStar` class for backward compatibility with legacy plugins.
- Added `register` decorator for legacy plugin metadata.
- Enhanced `MessageChain` class with `to_payload` and `is_plain_text_only` methods.
- Updated `AstrMessageEvent.send` method to utilize `send_chain` for rich messages.
- Implemented `send_chain` method in `PlatformClient` for sending complex message structures.
- Added capability routing for `platform.send_chain`.
- Introduced tests for new functionality, ensuring compatibility with legacy plugins and message handling.

src-new/astrbot_sdk/api/basic/astrbot_config.py

@@ -1,8 +1,43 @@
 """旧版配置对象兼容类型。"""
 
+from __future__ import annotations
+
+import json
+from pathlib import Path
+from typing import Any
+
 
 class AstrBotConfig(dict):
     """兼容旧版 ``AstrBotConfig``。
 
-    旧版实现本身就是 ``dict`` 的薄封装，兼容层保持这一行为。
+    旧版实现本身就是 ``dict`` 的薄封装。compat 层额外补上
+    ``save_config()``，以支持文档里的插件配置用法。
     """
+
+    def __init__(
+        self,
+        *args: Any,
+        save_path: str | Path | None = None,
+        **kwargs: Any,
+    ) -> None:
+        super().__init__(*args, **kwargs)
+        self._save_path = Path(save_path) if save_path is not None else None
+
+    @property
+    def save_path(self) -> Path | None:
+        return self._save_path
+
+    def bind_save_path(self, save_path: str | Path | None) -> "AstrBotConfig":
+        self._save_path = Path(save_path) if save_path is not None else None
+        return self
+
+    def save_config(self, save_path: str | Path | None = None) -> None:
+        path = Path(save_path) if save_path is not None else self._save_path
+        if path is None:
+            raise RuntimeError("AstrBotConfig 未绑定保存路径")
+        path.parent.mkdir(parents=True, exist_ok=True)
+        path.write_text(
+            json.dumps(self, ensure_ascii=False, indent=2, sort_keys=True),
+            encoding="utf-8",
+        )
+        self._save_path = path