VCG_sampler() now shortens long covariate names in
the target plot to a maximum of 11 characters, built from the first 8
characters + _ + the last 2 characters to keep them unique.
A warning is printed when names are cut.
VCG_sampler() now issues sanity warnings when
running: too many covariates (> 21), a small POOL size relative to
the number of covariates (ratio < 5, reported), and a requested VCG
size that is >= 75% of the POOL. When stratification is used, these
checks are reported per stratum, plus a warning is added when stratum
sizes are strongly imbalanced.
Covariate scaling now uses a robust median/MAD approach (falling
back to the standard deviation when the MAD is 0).
robust_scale() gained an optional group
argument (defaulting to NULL, using all observations) and
now backs the scaling in VCG_sampler(),
energy_distance(), combine_variables() and
find_outliers(), replacing base
scale().
Unit test added via testthat framework