modular: a^b)^c = a^(b * c). Which requires carmichael fn.

[github-actions]

On 2022-06-03 @recmo wrote in 2f6a5d6 “Merge pull request #103 from recmo/mulmod”:

a^b)^c = a^(b * c). Which requires carmichael fn.

            // TODO: Increase cases when perf is better.
            let mut config = Config::default();
            config.cases = min(config.cases, if BITS > 500 { 3 } else { 10 });
            proptest!(config, |(a: U, b: U, c: U, m: U)| {
                // TODO: a^(b+c) = a^b * a^c. Which requires carmichael fn.
                // TODO: (a^b)^c = a^(b * c). Which requires carmichael fn.
                assert_eq!(a.mul_mod(b, m).pow_mod(c, m), a.pow_mod(c, m).mul_mod(b.pow_mod(c, m), m));
            });
        });
    }
}

From src/modular.rs:182