style(all): limit docstring length

core/functions/tracks.py

core/processes/births.py

core/processes/knngraph.py

core/processes/leiden.py

core/processes/peaks.py

core/processes/picker.py

core/processes/savgol.py

core/processes/standardscaler.py

examples/basic_processes.py

examples/group.py

examples/testing.py

grouper.py

routines/heatmap.py

routines/mean_plot.py

routines/median_plot.py