Function dispatch_log_f32 

pub fn dispatch_log_f32(
    encoder: &mut CommandEncoder,
    registry: &mut KernelRegistry,
    device: &DeviceRef,
    input: &MlxBuffer,
    output: &MlxBuffer,
) -> Result<()>

Encode output[i] = log(input[i]) for f32 input.

Caller must ensure input is strictly positive — the kernel does not check; log(x ≤ 0) produces NaN or -inf per IEEE 754.