Minecarts Overhaul

Copper patina now comes from Additional Additions.

• Removed our own Patina item, its axe-scrape drop and the matching loot table. Additional Additions already adds a copper patina, and its version does everything ours did plus placing as a redstone-conducting block with recipes into cyan dye and a patina block. Running both dropped two competing patinas from the same scrape.
• Copper rails come out ahead: our drop was capped to full cubes at a 30% chance, so it never triggered on rails. The Additional Additions drop has no such restriction.
• Existing minecarts-overhaul:patina stacks will disappear when a world loads, since the item no longer exists.
• Adds the CI this repo was missing: a build check on pull requests and automatic Modrinth publishing from releases.

Built for Minecraft 26.1.2 with Fabric.