Restore extinct Superflat mobs via custom player-built habitats

Updates/bugs accidentally killed off 4 mobs and 5 core items on Superflat (Rabbits in 1.9, Squids in 1.13.1, Axolotls in 1.18, Glow Squids in 1.21). Tamed cats can gift hides/feet, but players are completely locked out of raw rabbit, stew, normal ink, and Glow Ink Sacs—killing access to glow item frames and glowing sign text for base organization. Instead of random spawning, we can bring them back by tying spawns to intentional, player-built habitats to keep the outer world empty: • Rabbits: Rare chance to spawn in Villages near mature carrot/potato plots. They act as "crop-stealing goobers", forcing players to protect the local ecosystem. • Normal Squids: Only spawn in pools 2+ blocks deep with a Coral block floor (renewable via Wandering Traders). This completely prevents them from clogging infinite water or cobble farms. • Glow Squids: Only spawn in total darkness (light level 0) at low Y-levels near Bedrock on a stone/deepslate floor. Statistical impossibility to ruin surface builds. • Axolotls: Only spawn in pools fully enclosed from the sky in total darkness, requiring a Clay block floor (renewable via mud drying/trial pots). Makes them a rewarding mid-to-late game milestone. Restoring these through custom infrastructure doesn't ruin the classic "empty" vibe—it perfectly rewards endgame engineering and lets players rescue these species. Please fix these unintended casualties of past updates!