Remnants: Roguelite Dungeons

Fixes

• Server freeze when a dungeon site loads. On 1.21.1, 26.1.2, 26.2 and 26.3 the server could stop permanently, with the client still rendering and quitting hanging, the first time a chunk holding a Meridian Archive site loaded. It was most likely with large world-generation packs. Site blocks were being placed from inside the chunk-load callback; they are now placed on the next server tick, the way 1.20.1 already did.
• Site blocks now wait until every chunk under the site is loaded, not only its four corners, so wide sites no longer force their middle chunks to load.