Adding statistical functions

[kevloui]

No description provided.

[kevloui]

Thank you for the fixes!

[alecmocatta]

Remember to add the user-facing .mean() method in par_pipe.rs and par_stream.rs

[alecmocatta]

.mean() needs to be exposed as a user-facing function in par_stream dn par_sink

[kevloui]

Added .stddev() and split stats.rs into mean.rs and stddev.rs for clarity.

[kevloui]

Changes to stddev.rs for pooled SD. General cleanup.

[alecmocatta]

Clippy gives a bunch of cast_precision_loss warnings. Could you possibly use these two methods in place of as to fix this?

#[allow(
	clippy::cast_possible_truncation,
	clippy::cast_sign_loss,
	clippy::cast_precision_loss
)]
fn u64_to_f64(x: u64) -> f64 {
	assert_eq!(x, x as f64 as u64);
	x as f64
}
#[allow(
	clippy::cast_possible_truncation,
	clippy::cast_sign_loss,
	clippy::cast_precision_loss,
	clippy::float_cmp
)]
fn f64_to_u64(x: f64) -> u64 {
	assert_eq!(x, x as u64 as f64);
	x as u64
}

To be extra neat perhaps you could put these in amadeus-core/src/util.rs and adjust amadeus-core/src/file/local.rs to use them as well?

Pull request has been modified.