fearless_simd + BRAVO

[Shnatsel]

I've cleaned up the PoC and made it adapt to the native vector width.

This is a significant performance improvement across the board, barring the smallest sizes on Aarch64 which worked well enough with fully unrolled paths specialized for a single small size.

This is also a way forward for writing code that's "generic" over the f32/f64 types and native vector widths. The machine code is the same as if these were Rust generics (full monomorphization) but it's implemented via declarative macros. We can reuse this approach for DiT kernels later, which are currently copy-pasted.

Stacked on top of #58

Supersedes #62

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.14815% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 99.79%. Comparing base (6875e8c) to head (c34cce2).

Files with missing lines	Patch %	Lines
src/algorithms/bravo.rs	98.07%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #64      +/-   ##
==========================================
- Coverage   99.88%   99.79%   -0.10%     
==========================================
  Files          12       13       +1     
  Lines        2711     2867     +156     
==========================================
+ Hits         2708     2861     +153     
- Misses          3        6       +3     

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