feat: sigma_1() function

[Autoparallel]

Requires #3

Another common permutation/compression function used in SHA-256 is commonly called $\Sigma_1$. It is implemented like so:

fn sigma_1(x: u32) -> u32 {
  rotate_right::<6>(x) ^ rotate_right::<11>(x) ^ rotate_right::<25>(x)
}

where rotate_right() is a circular bitwise rotation described in #3.