fn get_inner_hash(seed: &[u8; 32], grinding_factor: u8) -> [u8; 32] {
    let mut inner_data = [0u8; 41];
    inner_data[0..8].copy_from_slice(&PREFIX);
    inner_data[8..40].copy_from_slice(seed);
    inner_data[40] = grinding_factor;

    let digest = Keccak256::digest(inner_data);
    digest[..32].try_into().unwrap()
}
Returns the bit-string constructed as
Hash(prefix || seed || grinding_factor)
`prefix` is the bit-string `0x123456789abcded`
crates/provers/stark/src/grinding.rs