Fix type inference failure in get_clims

[BioTurboNick]

Resolves #3837

The intent is to short-circuit the clims calculation with a shape series type. Each shape is a series and only has a single color (right?), so all that calculation is unnecessary.

Only issue with the current PR is that using fill_z instead of fillcolor is broken, plot shapes have no color. Has to be a way to detect this situation to allow get_clims to work properly?

[BeastyBlacksmith]

Each shape is a series and only has a single color (right?)

I don't think so, you should be able to set the color of the border separate from the fillcolor and while not implemented we shouldn't block the way to fill shapes with gradients

[BioTurboNick]

Fair enough.

Taking a closer look, it seems that code is very type unstable, or inference failed. If I enforce the type of the return value as Tuple{Float64, Float64}, performance improves almost as much.

[codecov]

Codecov Report

Merging #3838 (37a6476) into master (0cd8124) will decrease coverage by 0.25%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3838      +/-   ##
==========================================
- Coverage   63.50%   63.25%   -0.26%     
==========================================
  Files          28       28              
  Lines        7464     7489      +25     
==========================================
- Hits         4740     4737       -3     
- Misses       2724     2752      +28     

Impacted Files	Coverage Δ
src/colorbars.jl	92.72% <100.00%> (+1.81%)	⬆️
src/utils.jl	52.85% <0.00%> (-1.93%)	⬇️
src/args.jl	73.46% <0.00%> (-0.58%)	⬇️
src/backends/pgfplotsx.jl	61.17% <0.00%> (-0.38%)	⬇️
src/backends.jl	63.47% <0.00%> (ø)
src/examples.jl	61.97% <0.00%> (ø)
src/backends/unicodeplots.jl	75.00% <0.00%> (ø)
src/backends/gr.jl	89.42% <0.00%> (+0.08%)	⬆️

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[t-bltg]

Nice, we should have more of these to be as type stable as possible.