[FEATURE] Fix and test `r_indicator` implementation

[neuralsorcerer]

balance/balance/stats_and_plots/weighted_comparisons_stats.py

Line 42 in 6d34f01

# TODO: fix the r_indicator function. The current implementation is broken since it

Investigate the current r_indicator logic, identify the failure mode, and implement a corrected version. Add unit tests covering typical use cases and edge cases (e.g., identical samples, extreme weight distributions).