Increase the speed in getting the standardized solution using `std_lav()`

[sfcheung]

Note

The bottleneck is in std_lav(). For steps that unnecessarily repeated in the *apply functions, do them once only.

To-Do

• [ ] Generate the mapping vectors between the lavaan model matrices and the RAM matrices.
• [ ] Revise std_lav() to do the step above only once.

[sfcheung]

Moved.