Complete plant shopping project

[srenge]

This pull request introduces several improvements to the shopping cart and product list functionality, focusing on better cart management, UI enhancements, and code quality. The main changes include refactoring the cart logic in Redux, displaying the cart quantity in the navigation bar, improving the product list rendering, and enforcing prop types for better component validation.

Cart functionality and Redux logic:

• Refactored addItem, removeItem, and updateQuantity reducers in CartSlice.jsx to properly handle item addition, removal, and quantity updates, ensuring items are only added once and quantities are updated correctly.
• Updated cart actions in CartItem.jsx to dispatch Redux actions for incrementing, decrementing, and removing items, and to calculate total amounts and costs more robustly.