💡 add utils docstring

docs/api/utils.md

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+---
+contentSidebar: true
+sidebarDepth: 0
+---
+
+# NoneBot.utils 模块
+
+
+## `run_sync(func)`
+
+
+* **说明**
+
+    一个用于包装 sync function 为 async function 的装饰器
+
+
+
+* **参数**
+
+    
+    * `func: Callable[..., Any]`: 被装饰的同步函数
+
+
+
+* **返回**
+
+    
+    * Callable[..., Awaitable[Any]]
+
+
+
+## _class_ `DataclassEncoder`
+
+基类：`json.encoder.JSONEncoder`
+
+
+* **类型**
+
+    `json.JSONEncoder`
+
+
+
+* **说明**
+
+    `JSONEncoder` used when encoding `Message` (List of dataclasses)
+
+
+
+### `default(o)`
+
+Implement this method in a subclass such that it returns
+a serializable object for `o`, or calls the base implementation
+(to raise a `TypeError`).
+
+For example, to support arbitrary iterators, you could
+implement default like this:
+
+```default
+def default(self, o):
+    try:
+        iterable = iter(o)
+    except TypeError:
+        pass
+    else:
+        return list(iterable)
+    # Let the base class default method raise the TypeError
+    return JSONEncoder.default(self, o)
+```