[Feat] SukiSideMenu with SubItems

[orangebobolink]

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Description of new feature

Each element in the SukiSideMenu can have one or more SubItem elements, allowing for a nested menu structure. This is useful for creating a user interface where menu items can be expanded to reveal additional options.
Example:

Package Version

6.0.0-rc

[xuxiaokang0723]

Hope the author can add this feature soon！