Kyber constant time division

[FAlbertDev]

Pull request dependencies

• #3887

This PR adds logic to perform constant-time division by replacing division with a multiplication and right-shift. Instead of using magic numbers for division and right-shift for the specific Kyber constant Q, we compute them on compile time using an algorithm from Hacker's Delight, Chapter 10 - 9.

Also, to ensure the algorithm's correctness, we added a test covering all possible numerators that may occur in Kyber's computation.

Commit: 58a9962

[coveralls]

coverage: 92.006%. remained the same when pulling 9bbdc6a5bcb8316f167428b376e81c3f8e3c2f28 on Rohde-Schwarz:kyber-ct-div into 13c7e5f1d29455bde2865fd287abc06e747fe389 on randombit:master.

[reneme]

Perhaps describe the counter measure in side_channel.rst?

[reneme]

Rebased and resolved conflicts after #3874 was merged and #3887 was adapted to it.

[FAlbertDev]

Closed. See #3959.