Implement compatible primitive roots of unity as powers of two

[Sword-Smith]

Cf. https://www.ingonyama.com/blogs/goldilocks-ntt-trick some of the primitive roots of unity can be implemented as powers of 2. This holds for the roots with order 4 to 64 (both inclusive).

With this trick, the new orders of unity become:

static PRIMITIVE_ROOTS: phf::Map<u64, u64> = phf_map! {
    2u64 => Q - 1,
    4u64 => 1u64 << 48,
    8u64 => 1u64 << 24,
    16u64 => 1u64 << 12,
    32u64 => 1u64 << 6,
    64u64 => 1u64 << 3,
    128u64 => 2198989700608,
    256u64 => 4404853092538523347,
    512u64 => 6434636298004421797,
    1024u64 => 4255134452441852017,
    2048u64 => 9113133275150391358,
    4096u64 => 4355325209153869931,
    8192u64 => 4308460244895131701,
    16384u64 => 7126024226993609386,
    32768u64 => 1873558160482552414,
    65536u64 => 8167150655112846419,
    131072u64 => 5718075921287398682,
    262144u64 => 3411401055030829696,
    524288u64 => 8982441859486529725,
    1048576u64 => 1971462654193939361,
    2097152u64 => 6553637399136210105,
    4194304u64 => 8124823329697072476,
    8388608u64 => 5936499541590631774,
    16777216u64 => 2709866199236980323,
    33554432u64 => 8877499657461974390,
    67108864u64 => 3757607247483852735,
    134217728u64 => 4969973714567017225,
    268435456u64 => 2147253751702802259,
    536870912u64 => 2530564950562219707,
    1073741824u64 => 1905180297017055339,
    2147483648u64 => 3524815499551269279,
    4294967296u64 => 7277203076849721926,
};

I think the NTT/INTT is only determined up to a constant so there might be some intermediate NTT results that are no longer valid.

[jan-ferdinand]

Do we still care about this in any way?