Function stft 

pub fn stft(
    signal: Tensor<2>,
    window: Option<Tensor<1>>,
    options: StftOptions,
) -> Tensor<4>

Computes the Short-Time Fourier Transform (STFT).

Splits the signal into overlapping windowed frames and computes the FFT on each.

Returns

A tensor of shape [batch, n_frames, n_freqs, 2] where the last dimension holds [real, imaginary].