[Bug] messages_zh.yml / messages_nl.yml duplicate keys and structural defects #80

Bug description

Several defects in the bundled messages_zh.yml and messages_nl.yml files make parts of the shop UI render with English fallback text (or empty), and log a startup warning.

1. Duplicate shop.common keys — both files define shop: twice; SnakeYAML (Bukkit's default) keeps only the last block, so the first 8 keys (buy-line, sell-line, shift-click-line, cannot-sell-line, buy-only-shift-line, spawner-display-name, item-display-name, menu.fill-display-name) are silently lost, and the server logs [WARN]: duplicate keys found : common.
2. shop.shop.rotations double nesting — daily-special texts live under shop.shop.rotations.* instead of shop.rotations.*, so the rotation system never resolves them.
3. shop.stock.gui.see-all.lore is a list — stock-gui.yml references see-all.lore.line1 / see-all.lore.line2 via {translate:...} macros, which a list-typed value cannot satisfy.
4. messages_nl.yml missing live stock-GUI keys — shop.stock.gui.filters.*, shop.stock.gui.pagination.*, and shop.stock.gui.localization.item-price-format / item-blocked / item-frozen / no-items are absent (present only under all-stocks), so those spots render empty in Dutch.

Fix

Branch fix/messages-files on fork OrzMC/EzShops:

• Merges the duplicated shop.common blocks to a single one (text unchanged).
• Un-nests shop.shop.rotations to shop.rotations (zh and nl).
• Converts see-all.lore from a list to a line1 / line2 map (zh and nl).
• Adds the missing shop.stock.gui keys to nl.
• Adds a regression test MessageFilesDuplicateKeyTest that parses all four messages_*.yml files in strict mode (allowDuplicateKeys = false), so CI catches any future duplicate keys.