Add Rust reference & AVX code, test and benchmark suites

[0.2.0] - 2025-09-15

Breaking changes

• Updated the trait FillUniform to take log_bound.

poulpy-hal

• Added pure Rust reference code for vec_znx and fft64 backend.
• Added cross-backend generic test suite along with macros.
• Added benchmark generic test suite.

poulpy-backend

• Added FFTRef backend, which provides an implementation relying on the reference code of poulpy-hal.
• Added FFTAvx backend, which provides a pure Rust AVX/FMA accelerated implementation of FFTRef backend.
• Added cross-backend tests between FFTRef and FFTAvx.
• Added cross-backend tests between FFTRef and FFT64Spqlios.

poulpy-core

• Removed unsafe blocks.
• Added tests suite for FFTRef and FFTAvx backends.

Other

• Fixed a few minor bugs.