Additional formulas for Mana generation

[oliviasaa]

Request from Chloé:

Is there a way to, given a generation amount, stored mana, and required mana

• determine whether the generation amount will generate faster than the stored mana decays?
• and if it will, determine how many slots it will take to generate mana >= required_mana?

[oliviasaa]

It is not a difficult formula to find, but it was placed in the product backlog for now.