Turn `bounding_box` class to function

[atteggiani]

The bounding_box class:

https://github.com/ACCESS-NRI/replace_landsurface/blob/2dcc1d77ca4fb7d4dcb6311db575bd2b21d700b4/src/replace_landsurface_with_ERA5land_IC.py#L37-L115

ultimately, is used to get the extents of the input file in terms of min and max longitudes and latitudes (lonmin, lonmax, latmin and latmax).

The class does not currently hold any methods (apart from the __init__) or attributes apart from the lat/lon extents it needs to produce.

I suggest turning it into a function to:

• simplify the code
• simplify testing

[truth-quark]

Indeed, the single method/__init__ only class is a sign of unclear design. Also, __init__ is doing multiple things: file I/O, lat/long calcs, control flow, array ops & setting member vars. It's a sign to break down the problem into smaller pieces.

Shapely may suit for providing generic geometry data structures too: https://shapely.readthedocs.io/en/stable/manual.html