add test for astrog difference plot

[veenstrajelmer]

Plotting testcase:

import hatyan
import pandas as pd

start_date_utc = pd.Timestamp(2000, 1, 1, tz="UTC")
end_date_utc = pd.Timestamp(2000, 4, 1, tz="UTC")

culminations_python = hatyan.astrog_culminations(tFirst=start_date_utc, tLast=end_date_utc)
culminations_python_naive = culminations_python.copy()
culminations_python_naive['datetime'] = culminations_python_naive['datetime'].dt.tz_localize(None)

fig, (ax1,ax2,ax3) = hatyan.plot_astrog_diff(culminations_python, culminations_python_naive, typeLab=['lower','upper'], timeBand=[-.18,.18])