Added optional precompute parameter in FFT domain initialization

[ThomasPiellard]

This PR fixes #36 a performance loss of the FFT which occurred when the support of arbitrary cosets was added.

Description

When creating an FFT domain, a boolean value is now passed as parameter to force some pre computations, namely the BitReverse of the coset table. Forcing the pre computing or not is a time/memory trade off. Forcing the pre computations doubles the memory needed to stored a domain.

API breaking changes

func NewDomain(m, depth uint64, precomputeReversedTable bool) *Domain
instead of:
func NewDomain(m, depth uint64) *Domain

Benchmarks

MBP 2.2GHz 6-core i7 - 16GB RAM

BenchmarkFFT/fft_2**18bits_(cosets_without_precomputations)-12                48          20933738 ns/op
BenchmarkFFT/fft_2**18bits_(cosets_with_precomputations)-12                   96          12964353 ns/op

[CLAassistant]

All committers have signed the CLA.

[gbotrel]

Looks good to me, merging. May revisit with optimization work on Consensys/gnark/issues/69