Function generate_ring_positions 

pub fn generate_ring_positions<F>(
    seed: i64,
    distance: i32,
    spread: i32,
    count: i32,
    snap_biome: Option<&F>,
    thread_pool: &ThreadPool,
) -> Vec<ChunkPos>
where
    F: Fn(i32, i32, &mut LegacyRandom) -> Option<(i32, i32)> + Sync,

Vanilla’s ChunkGeneratorStructureState.generateRingPositions. Positions in chunk coords. If snap_biome is provided it gets (block_x, block_z, &mut rng) and returns Some((snapped_block_x, snapped_block_z)) to snap, or None to keep raw.