Describe the bug
A clear and concise description of what the bug is.
You are able to put a backpack inside of a shulker, and a shulker inside of a backpack. Thus creating an 'infinite capacity storage'.
To Reproduce
Steps to reproduce the behavior:

1. Uh...described above

Expected behavior
A clear and concise description of what you expected to happen.
I'd expect you to not be able to either
A: Put a backpack into a shulker
B: Be able to put a shulker into a backpack
Screenshots
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Required informations (please complete the following information):

• Mod version: 1.19.2-8.2.1
• Mod Loader: Fabric

Additional context
Add any other context about the problem here.

For the dev to solve this easily, they can make the backpack item override this canFitInsideContainerItems method to return true and make their backpack’s item slots check and reject any item that returns true for that method
https://github.com/TelepathicGrunt/Bumblezone/blob/db7d29cd8e02466bd01d8ea697cd22b09a57601d/src/main/java/com/telepathicgrunt/the_bumblezone/items/BzBlockItem.java#L21

This will prevent backpacks from being put into shulker boxes and prevent shulker boxes from being put into backpacks. Thus breaking the infinite storage issue. Other mods with shulker box-like items should also be doing the same to prevent infinite nesting as well. My Bumblezone mod’s honey cocoon does the same so this change would work with Bumblezone too.

Thank you @TelepathicGrunt didnt know about this useful method, backpacks won't be placeable in shulkerboxes

https://www.curseforge.com/minecraft/mc-mods/travelers-backpack-fabric/files/all
Available for Fabric
(Forge soon)

https://www.curseforge.com/minecraft/mc-mods/travelers-backpack/files