What this mod does

Adds upgrade tiers for Wearable Backpacks.
Higher tiers can have more slots, optional higher stack caps, bauble integration, inventory preview, and fire immunity.

Backpack tiers

Diamond and above disable Encumbered while worn.
Obsidian and Enchanted backpacks are fire immune.
Obsidian and above can be removed from Baubles slots even when they contain items.
Enchanted backpacks have a visual enchantment glint.
Hold Shift + Ctrl while hovering a backpack in your inventory to preview its contents. This works from Copper tier upward when inventory preview is enabled.

Higher stack caps are controlled by config.
If higher stack caps are disabled, backpacks stay at normal vanilla stack behavior.
Maximum supported stack cap is 127.

Normal -> Copper: alternate 4 copper ingots and 4 copper blocks. Both checkerboard orientations work.
Copper -> Bronze: alternate 4 bronze ingots and 4 copper blocks.
Bronze -> Silver: alternate 4 silver ingots and 4 silver blocks.
Silver -> Iron: alternate 4 iron ingots and 4 iron blocks.
Iron -> Gold: alternate 4 gold ingots and 4 gold blocks.
Gold -> Diamond: alternate 4 diamonds and 4 diamond blocks.
Diamond -> Obsidian: surround backpack with 4 obsidian and 4 shulker shells, alternating around the backpack.
Obsidian -> Enchanted: use glowing ingots plus one glowing gem.

Bauble integration must be enabled in config.
Use an anvil: backpack + compatible bauble.
Integrated baubles count against the backpack tier's bauble slots.
Duplicate integrations are not allowed.
Slime Ball on an anvil removes the oldest integrated bauble. You are sliming them.
Glowing Gem on an anvil extracts the newest integrated bauble and destroys the anvil.

enableHigherStackCap: allows stack caps above 64.
enableUnstackableHigherCap: allows normally unstackable items to stack in backpacks.
enableBauleFusion: enables bauble integration.
enableInventoryPreview: enables Shift+Ctrl inventory preview.