Fix evaluation of dense polynomials over domains smaller than the degree

[tjade273]

Fixes the evaluation of dense polynomials over domains smaller than the polynomial degree.

Currently, the coefficients of dense polynomials are truncated to match the size of the evaluation domain. This causes unexpected / incorrect behavior when larger polynomials are used. This PR resolves the issue by reducing the polynomial mod X^d where d is the size of the domain, before the FFT is performed.

A new unit test is located in src/polynomial/univariate/sparse.rs

It may also be a good idea to throw an error in the FFT routine when the coefficient vector is bigger than the FFT size, so that information is not accidentally discarded.

closes: #520

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• Wrote unit tests
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[Pratyush]

Suggested change

	x.iter().zip(y).map(|(&x, y)| x + y).collect()
	cfg_iter!(x).zip(y).map(|(&x, y)| x + y).collect()

[Pratyush]

Actually, can avoid extra allocations here by making this a for loop, like so:

let mut reduced = chunks.next().unwrap();
for chunk in chunks {
    cfg_iter_mut!(reduced).zip(chunk).for_each(|(x, y)| {
    *x += y;
});
}

[tjade273]

Thanks for the notes, should be better now.

[Pratyush]

Thanks for the fix. Just left a small comment.