Calculates the log of Wilks' lambda statistic
for a given super_sample object.
This function ensures that the within-group
and total covariance matrices are computed,
then computes the difference of their log determinants.
log_wilks_lambda(super_sample)A numeric value representing the log Wilks' lambda statistic.
An object of class CSuperSample
Wilks' lambda is a test statistic for the ANOVA test decribed in (to appear)