Add 2D Gaussian fitter to qlook commands

[ShinjiFujita]

Closes #187.

[astropenguin]

Thank you for the update! I would like to ask you to fix the following things:

• Package imports (L30-32): We put standard library under # standard library and external dependencies under # dependencies. Could you put import copy under # standard library (L14) and from scipy.optimize import curve_fit under from matplotlib.figure import Figure (L28)? Also, could you remove import pandas as pd as it is not used anymore in this module?
• data[data != data] = 0.0 (L230, 489): Is it supposed to replace NaN values with zero? If so, could you consider to use data[np.isnan(data)] = 0 as it is more intuitive?
• cont_fit = ... (L255, 514): The variable name cont_fit is a bit ambiguous because cont in this context sounds like not only continuum but also contours. Since this variable is not used throughout the function, could you simply remove this?
• Code comments (L264-268, 523-527): Could you remove these lines? We manage the code changes by Git, so you do not need to leave the unused codes as comments.
• If-else block (L269-288, 528-547): You do not need to do this because min_frequency and max_frequency are strings with explicit units. You can simply code like f"min_frequency: {min_frequency}, max_frequency: {max_frequency}".

[astropenguin]

Thank you for the fix! Could you please fix the two minor remaining things?

• Could you put import copy just below # standard library (L14)? In general, import something should be placed above from module import something.
• Could you remove cont_fit (L497)?

[astropenguin]

Thank you so much! It looks good for me, so I will merge it into main.