fix(content): Fix double flooring for magic defence formula

[tannerdino]

Separation of 'style bonus' and +8 from ~combat_effective_stat, makes it easier to implement void in the future... Restructuring it in a way where style bonuses are applied at the end prevents us from having to -8 to $effective magic and $effective_defence, for effective magic defence.

Our previous effective magic defence would double floor since we used scale(). Now the question is, did jagex implement the 30/70 split like:
divide(add(multiply(7, $effective_magic), multiply(3, $effective_defence)), 10);
or
add(scale(3, 10, $effective_defence), scale(7, 10, $effective_magic));

My guess is without scale(). this will only have very minor differences