Floating-Point Testing with Z3

[JJponce0913]

This PR introduces a script that utilizes the Z3 SMT solver to verify the correctness of floating-point properties across different rounding modes. The goal is to test all rules considered FP-safe and identify cases where exceptions occur.

This PR improves floating-point safety analysis by giving us the ability to detect rounding-related issues, ensuring reliability in FP computations.

[bksaiki]

Might be good to nest again, say

docs
|-- fp-safe
     |-- z3test.py
     |-- README.md

Otherwise, looks good to me!