Function inventory_menu 

pub fn inventory_menu(inventory: Shared<PlayerInventory>) -> Menu

Builds the player inventory menu, always open when no other menu is.

The inventory container should contain:

• Slots 0-35: Main inventory (hotbar 0-8, main 9-35)
• Slots 36-39: Armor (feet, legs, chest, head)
• Slot 40: Offhand