Ultra Fast Pregen

Fixed

• Bright caves next to loaded chunks: chunks the server had only started generating when a batch reached them were lit as if they had no blocks: sky light 15 everywhere underground and no light from lava, so their caves showed bright. These are the ring of partly generated chunks, about 11 chunks wide, around the spawn chunks, players and force-loaded chunks. A run centered on spawn, or near a player (always the case in singleplayer), crossed such a ring. Those chunks are now lit from their generated blocks like every other chunk. Runs away from loaded chunks were not affected.
• Worlds generated with 14 around spawn or players: Minecraft relights every chunk after "Erase cached data": in singleplayer, Edit World → Optimize World with "Erase cached data" ticked; on a server, start it once with --forceUpgrade --eraseCache. Deleting the affected chunks so they generate again works too.