Add option to preserve 0–360 longitude convention (--keep_longitude)

[RonaldRN]

This pull request introduces an option to preserve the original longitude convention (0–360) when processing data.

Motivation:
Cyclones crossing the dateline can be difficult to track and visualize when longitudes are automatically converted to -180 to 180. Keeping the original convention simplifies domain selection, tracking, and visualization, especially for systems near 180°.

Main changes:

• Adds the --keep_longitude flag to preserve 0–360 longitude format
• Maintains backward compatibility (default behavior unchanged)
• Improves usability for dateline-crossing systems

Usage example:

bash
python atmos_bud.py input.nc -c --keep_longitude

[RonaldRN]

Additional updates included:

• Implements interactive box selection (click-and-drag) to extract cyclone coordinates
• Outputs time, latitude, longitude, length, and width
• Preserves longitude convention (0–360 or -180–180), handling dateline-crossing systems
• Adds continent boundaries using shapefile input
• Supports variable and pressure level selection

Usage examples:
python Extract_coords_time-lat-lon-length-width.py input.nc --shp shapefile.shp --out track_cyclone.txt
python Extract_coords_time-lat-lon-length-width.py input.nc --shp shapefile.shp --var z --level 850 --out track_850.txt