In the `hint_k256_inverse_field_10x26` and `hint_k256_sqrt_field_10x26`
functions, this PR ensures that the returned result actually consists of
26 bits limbs, as the name suggests. (Except for the most significant
limb, which is 22 bits.) This means that the field element is weakly
normalized and can be used safely by the guest program.
When the input is non-square, the prover returns the square root of the
input times a predefined non-quadratic residue.
The idea is that the guest should also prove the non-square case, so it
must check that:
`result * result == input * PREDEFINED_NON_QR`.
Chose `3` as the predefined non_qr.
