Add m_includeZeroValues option to RimEnsembleStatistics (default on, preserving existing behavior). When disabled, exact zero values (e.g. from shut-in wells/groups) are excluded from the mean, P10/P50/P90 and custom percentile calculations in RimEnsembleStatisticsCase::calculate(). This is useful for derived vectors such as WCT, GOR and PI, where zeros caused by a shut well/group should not skew the statistical curves.
Exact equality (not an epsilon) is used, since shut-in values are reported as exact 0.0 by the simulator and non-accumulated vectors use STEP_RIGHT interpolation, which does not introduce floating-point noise.
