Function modulate_oqpsk 

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

Modulates packed bits to OQPSK at 2× the symbol rate.

Maps consecutive bit pairs to I/Q values (±1/√2), then staggers them: I transitions at even sample indices, Q at odd indices.

n_bits must be even. Writes n_bits samples each to symbols_i and symbols_q.