Function hilbert_transform 

pub fn hilbert_transform(signal: &[f64]) -> Result<Vec<Complex64>>

Compute the Hilbert transform of a real signal via FFT.

Returns the analytic signal x(t) + i·H[x](t) as a length-N complex vector. The real part is the input; the imaginary part is the Hilbert transform. Uses circular boundary conventions; expect mild wrap-around artifacts at the first/last few samples for non-periodic input.