(fix: #672): Sidebar items expander should be cursor pointer

[Pradipram]

Fixed: Sidebar items expander should be cursor pointer

Screenshots

https://github.com/CircuitVerse/Interactive-Book/assets/101059602/90026395-5ad1-4eb2-8285-4d8be81cdb4a

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• [x] Reviewed the contributing guidelines 🔍️
• [x] Sample preview link added (add the link(s) for all the pages changed/updated from the checks tab after checks complete)
• [x] Tried Squashing the commits into one

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