support for high-dpi WebMap services

[raphaelquast]

At the moment WebMap services that provide tiles at non-standard dpi are not fetched correctly...

The issue originates most probably from somewhere in here (maybe some kind of a tilePixelRatio needs to be implemented
to take care of the different tile-sizes?)

EOmaps/eomaps/_webmap.py

Lines 1193 to 1197 in 76a1ef0

	located_images = self.raster_source.fetch_raster(
	ax.projection,
	extent=[x1, x2, y1, y2],
	target_resolution=(window_extent.width, window_extent.height),
	)

Here's an example for a high-dpi (512 instead of 96) wms service that does not work as expected...

from eomaps import Maps
m = Maps(Maps.CRS.GOOGLE_MERCATOR)
m.set_extent_to_location("wien")
m.add_wms.Austria.AT_basemap.add_layer.bmaphidpi()

# the corresponding normal dpi services works just fine
# m.add_wms.Austria.AT_basemap.add_layer.geolandbasemap()

Any help with this is highly appreciated!