Use stub file to keep class CommandGroup clean

nonebot/command/group.pyi

@@ -0,0 +1,24 @@
+from typing import Union, Callable, Iterable
+
+from nonebot.typing import CommandName_T
+
+
+class CommandGroup:
+    """
+    Group a set of commands with same name prefix.
+    """
+
+    __slots__ = ('basename', 'base_kwargs')
+
+    def __init__(self, name: Union[str, CommandName_T], *,
+                 permission: int = ...,
+                 only_to_me: bool = ...,
+                 privileged: bool = ...,
+                 shell_like: bool = ...): ...
+
+    def command(self, name: Union[str, CommandName_T], *,
+                aliases: Iterable[str] = ...,
+                permission: int = ...,
+                only_to_me: bool = ...,
+                privileged: bool = ...,
+                shell_like: bool = ...) -> Callable: ...