feat: add mix likelihood FCN
sum ln Li = sum ( sum ln Pj - ln sum Pk)
=> sum ln Pij - sum (ln sum Pk)
combine data int fitting a same model, reduce about 30% time.
sum ln Li = sum ( sum ln Pj - ln sum Pk)
=> sum ln Pij - sum (ln sum Pk)
combine data int fitting a same model, reduce about 30% time.