Add a ManifoldsBaseMakie extension

[kellertuer]

so that the checks, e.g. for retractions or geodesics – or the gradient in Manopt, can also be done with Makie instead of Plots.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (eae3060) to head (8445cd0).

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #272   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           33        34    +1     
  Lines         3771      3802   +31     
=========================================
+ Hits          3771      3802   +31     

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[mateuszbaran]

Judging by the error I think we need to use CairoMakie on CI instead of GLMakie.

[kellertuer]

Nice, the concept and the test ideas even work.

The remaining 4 lines are currently impossible to cover, since that method is overwritten (actually by both the Plots and the combined extension) which causes warnings anyways, so I have to change that a bit;
will try the idea that the plot functions (plot_slope and plot_check_geodesic) change their interface and have a Val{Symbol} as first parameter). This is fine, since that function is anyways an internal function.

[kellertuer]

Uff, this is quite tricky to get right, that loading a plotting package it “just works” we do not have exponential growth in extensions and we do not overwrite existing methods. Somewhere I might still have a quadruple knot in my thoughts by now. But I tried for several hours to get it right.

Ah. Changing variables within therein package from the extension does not have a persistent effect, it is basically not set. Interesting to know.
Then I have to rethink the logic a bit, since it is then a bit harder to have in mind which of the extensions to use.