utils/ consistency pass — naming, private ctors, consolidation

Pass over utils/ for consistency:

• Dissolve ShopBlockUtil (findNeighbor + face constants) into BlockUtil; dissolve the now-trivial ImplementationAdapter (Paper snapshot pass-throughs) into BlockUtil.getState + InventoryUtil.getHolder/getLeftSide/getRightSide.
• Rename Messages -> MessageUtil for suffix consistency.
• Add missing private constructors + final to the pure-static utils (BlockUtil, LocationUtil, NameUtil, NumberUtil, PriceUtil, QuantityUtil, StringUtil).
• Kept: Permissions (permission-node constants registry, not a generic helper bag), SimpleCache (generic utility type), and the cohesive domain utils kept separate (NumberUtil vs PriceUtil vs QuantityUtil; StringUtil vs NameUtil vs LocationUtil).

Follow-ups (separate): AdminInventory is a stateful 38-method Inventory impl mislocated in utils/ (needs re-engineering); FileFormatter/java.util.logging should migrate to slf4j like the sibling plugins.