Function modulate_8psk 

pub fn modulate_8psk(
    bits: &[u8],
    n_bits: usize,
    symbols_i: &mut [f32],
    symbols_q: &mut [f32],
)

Modulates packed bits to 8PSK I/Q symbols.

Groups n_bits into 3-bit chunks (MSB-first), maps each through the Gray-coded constellation, and writes one I/Q pair per symbol. n_bits must be a multiple of 3.

Writes n_bits / 3 samples to each of symbols_i, symbols_q.