Modify FFT implementation for SIMD backend

[andrewmilson]

This change is 

[andrewmilson]

• Add benchmarks for SIMD fft #609
• Add benchmarks for SIMD quotients #608
• Add benchmarks for SIMD eval_at_point #607
• Add benchmarks for SIMD bit_reverse #606
• Implement QuotientOps for SIMD backend #605
• Implement AccumulationOps for SIMD backend #604
• Implement FriOps for SIMD backend #603
• Implement PolyOps for SIMD backend #599
• Modify FFT implementation for SIMD backend #596 👈
• Add FFT implementation for SIMD backend #602
• Modify blake2s implementation for SIMD backend #595
• Add blake2s implementation for SIMD backend #601
• Modify bit_reverse for SIMD backend #594
• Add bit_reverse for SIMD backend #600
• Implement FieldOps for SIMD backend #593
• Add SIMD backend arithmetic #592
• Enable 'rng.gen()'ing field types #591
• dev

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 99.09297% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 92.12%. Comparing base (25bf368) to head (3b38213).
Report is 3 commits behind head on dev.

Files	Patch %	Lines
crates/prover/src/core/backend/simd/fft/ifft.rs	99.00%	1 Missing and 1 partial ⚠️
crates/prover/src/core/backend/simd/fft/rfft.rs	99.09%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #596      +/-   ##
==========================================
+ Coverage   91.98%   92.12%   +0.13%     
==========================================
  Files          80       80              
  Lines       10916    11275     +359     
  Branches    10916    11275     +359     
==========================================
+ Hits        10041    10387     +346     
- Misses        806      821      +15     
+ Partials       69       67       -2     

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[spapinistarkware]

Reviewable status: 0 of 4 files reviewed, 1 unresolved discussion (waiting on @andrewmilson)

a discussion (no related file):
It would be easier to check this Pr if you first add a commit that only copies the old files, so we can see in Reviewable just what changed.

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[spapinistarkware]

Reviewed 2 of 4 files at r3, 2 of 2 files at r4, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @andrewmilson)

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crates/prover/src/core/backend/simd/fft/mod.rs line 40 at r4 (raw file):

                    continue;
                }
                let val0 = load(values.add(i << 4).cast_const());

Consider inlining load() and store()

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crates/prover/src/core/backend/simd/fft/rfft.rs line 343 at r4 (raw file):

/// unreduced form, [0, P] including P. twiddle_dbl holds 16 values, each is a *double* of a twiddle
/// factor, in unreduced form, [0, 2*P].
pub fn butterfly(

butterfly() is a generic function that exists already, I want to not confuse them

Suggestion:

simd_butterfly