Rossby wave breaking indices from ERA5

The details of the implementation can be found in the documentation to the code that produced the data, in the module "geospatial.py". Data source is ERA5, potential vorticity on 320, 330, 340 and 350K in the Euro-Atlantic sector. From there, the PV=2PVU contours are extracted using the contourpy package. From the contours, PV overturnings (Barnes and Hartmann 2012) and PV streamers (Wernli and Sprenger 2007) are extracted, closely following the implementation in Severin Kaderli's master thesis and code (2024). The event objects are interpolated back onto the ERA5 grid optionally, and properties such as mean PV and mean eddy momentum flux in the area described by the event are also provided.