Add calc_ntr and make an enabler for cell_cycle_score

[Ukyeon]

1. create a _calc_ntr function and call it within the Monocle recipe.
2. Add a cell_cycle_score_enable parameter to allow users to enable the function.
3. Make a minor fix by removing the line that raises a NotImplementedError in the cell_cycle_score function, which always causes an error with the default parameter 'show'.

[Sichao25]

Could you also add the parameter experiment_type to the Preprocessor.preprocess_adata() ? I think that could be helpful.

[Xiaojieqiu]

_calc_ntr and cell_cycle_score_enable can be called for different recipes right?

[Ukyeon]

Calculation of calc_ntr and enabling cell_cycle_score can be utilized in different recipes, but they are currently not called within the existing code. Would you like to consider enabling them by default in the current operation?