plot_pie_sum raises ValueError: too many values to unpack (expected 4) on every call

src/graphing/plotting.py:101 unpacks 4 return values from filter_and_group, but that
function returns 5 (timestamp_groups, datapoint_groups, group_labels, colors,
alphas — see src/filter_and_group.py:52). Every other caller in plotting.py
correctly uses ..., colors, _ =.

Any call to plot_pie_sum fails immediately:
ValueError: too many values to unpack (expected 4)

Start in src/graphing/plotting.py at line 101 in plot_pie_sum and compare its filter_and_group unpacking with the other callers in that file. Check src/filter_and_group.py:52 for the five returned values. Done means plot_pie_sum no longer raises the unpacking ValueError on a normal call.

Written by the indexing model from the issue text.