feat: add DIT FFT algorithm & bit reversal control

[smu160]

add DIT FFT algorithm & bit reversal control

This PR introduces two major enhancements to PhastFT:

1. DIT (Decimation-in-Time) FFT algorithm - A complete alternative implementation to the
   existing DIF algorithm
2. Bit reversal control for DIF - Allows users to skip bit reversal for better performance
   when chaining operations

Changes

DIT FFT Implementation

• Complete DIT algorithm for both f32 and f64 precision
• Optimized SIMD kernels for chunk sizes 8, 16, 32, and 64
• Dedicated planners with pre-computed twiddle factors
• Runtime CPU feature detection via multiversion

Bit Reversal Control

• New Options::dif_perform_bit_reversal flag
• Conditional bit reversal in DIF algorithms
• Maintains backward compatibility (defaults to true)
• Note: this only affects DIF, not DIT

API Additions

pub fn fft_32_dit(reals: &mut [f32], imags: &mut [f32], direction: Direction)
pub fn fft_64_dit(reals: &mut [f64], imags: &mut [f64], direction: Direction)
pub fn fft_32_dit_with_planner(...)
pub fn fft_64_dit_with_planner(...)
pub fn fft_32_dit_with_planner_and_opts(...)
pub fn fft_64_dit_with_planner_and_opts(...)

[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.51282% with 28 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.22%. Comparing base (aa296ba) to head (c4450a9).

Files with missing lines	Patch %	Lines
src/algorithms/dit.rs	78.18%	24 Missing ⚠️
src/algorithms/dif.rs	50.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #37      +/-   ##
==========================================
- Coverage   99.12%   97.22%   -1.90%     
==========================================
  Files           8       12       +4     
  Lines         683     1225     +542     
==========================================
+ Hits          677     1191     +514     
- Misses          6       34      +28     

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