Optimized methods for squaring in extension fields of degree 2 & 3

[Al-Kindi-0]

This PR implements more optimized methods for computing squares in the degrees 2 and 3 extension fields. This is in contrast to the old way of squaring which was using a generic multiplication.
Also included, is a method for multiplying field elements in 64-bit field with constants smaller than $2^{32}$. This will be useful for extension fields that are defined by irreducible polynomials of the form $X^d - \omega$ where $d$ is the degree of the extension and $\omega$ is a field element. In the case of such extension fields, reduction modulo $X^d - \omega$ becomes just a multiplication by $\omega$ and thus a method for multiplying with small constants will be useful.

[irakliyk]

All looks good! Thank you!