merge for v8.2

[raphaelquast]

A new minor release with some fixes, many improvements to the internals and a few new features!

🌳 New

• You can now use m.add_colorbar(layer=..) to override the layer at which the colorbar is plotted
• There is a new method m.set_shade_dpi(...) to override the dpi used by shade-shapes. (Useful to fix data aggregation resolution for high-dpi exports or to adjust resolution to better suit data density)

🌦️ Changes

• Grid-snapping of the LayoutEditor now snaps to all edges of the axes (Useful in case the axis-size is not a multiple of the grid-spacing)
  • If multiple axes are moved, the first selected object acts as anchor
• The default matplotlib keymap p : "toggle pan/zoom tool" is now active again

🌩️ Internals (no effects on the public API)

• Unit-tests now use image-comparison to ensure stable image export results
• The Maps class has been refactored (Maps and MapsBase) to make the code more accessible and easier to handle.

🔨 Fixes

• fix handling of axes on combined layers in the LayoutEditor
• allow custom scatter_points marker shapes for "mark" callback
• fix issues with identification of grid-label position with projections that create non-intersecting grid-lines
• always print basic exception info on issue during layer-change action
• make sure to trigger a figure-update after adding a scalebar
• address pyproj warnings for pyproj>=3.5

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 74.39394% with 169 lines in your changes are missing coverage. Please review.

Project coverage is 75.29%. Comparing base (034ce66) to head (2aa99c9). Report is 2 commits behind head on master.

Files	Patch %	Lines
eomaps/_maps_base.py	77.49%	122 Missing :warning:
eomaps/_data_manager.py	42.85%	36 Missing :warning:
eomaps/helpers.py	16.66%	5 Missing :warning:
eomaps/_blit_manager.py	57.14%	3 Missing :warning:
eomaps/colorbar.py	85.71%	1 Missing :warning:
eomaps/layout_editor.py	95.45%	1 Missing :warning:
eomaps/scalebar.py	83.33%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #239 +/- ## ======================================= Coverage 75.29% 75.29% ======================================= Files 26 27 +1 Lines 11754 11817 +63 ======================================= + Hits 8850 8898 +48 - Misses 2904 2919 +15 ```

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