Fix caching logic

[1robie]

This pull request introduces a refinement to how item stacks are cached by adding a check for dynamic materials, ensuring that items with dynamic or placeholder-based materials are not cached prematurely. The main changes are:

Caching logic improvements:

• Added a new method isDynamicMaterial() to ZMenuItemStack to determine if an item's material is dynamic by checking for placeholders (%) or special material syntax (:), and verifying if the material loader is present.
• Updated the caching condition in MenuItemStackLoader to prevent caching of item stacks with dynamic materials, avoiding potential issues with items that require runtime evaluation.