Constant BABYBEAR_RC16_EXTERNAL_INITIAL 

pub const BABYBEAR_RC16_EXTERNAL_INITIAL: [[BabyBear; 16]; 4];

Initial round constants for the 16-width Poseidon2 external layer on BabyBear.

See https://github.com/HorizenLabs/poseidon2/blob/main/plain_implementations/src/poseidon2/poseidon2_instance_babybear.rs