Add vlplot option mindiameter

[pablosanjose]

VegaLite struggles with complex plots. This is a problem when plotting eigenstates of large systems. The situation can be alleviated when the eigenstates have many values very close to zero encoded with sitesize in vlplot that in principle should not be plotted. However, to make vlplot faster it is necessary to explicitly exclude these table entries from the data passed to @vlplot.

This PR allows one to exclude these entries by passing a mindiameter, that is complementary to maxdiameter. For it to be useful for performance it probably needs to be used together with plotlinks = false.

Without mindiameter (slow)

vlplot(h, ψ, sitesize = abs, plotlinks = false)

With mindiameter (fast)

vlplot(h, ψ, sitesize = abs, plotlinks = false, mindiameter = 1)

This PR adds an unrelated enhacement that allows to pass ψ as a Subspace (as produced e.g. by spectrum). If the subspace is degenerate, the first component is plotted for the moment. In the future we would need to sum over base components.

It also includes a fix for ArnoldiPackageMethod (blush!)

[codecov-io]

Codecov Report

Merging #138 (332c73f) into master (7dad499) will decrease coverage by 0.13%.
The diff coverage is 40.62%.

@@            Coverage Diff             @@
##           master     #138      +/-   ##
==========================================
- Coverage   61.16%   61.03%   -0.14%     
==========================================
  Files          16       16              
  Lines        2959     2972      +13     
==========================================
+ Hits         1810     1814       +4     
- Misses       1149     1158       +9     

Impacted Files	Coverage Δ
src/Quantica.jl	100.00% <ø> (ø)
src/plot_vegalite.jl	0.00% <0.00%> (ø)
src/diagonalizer.jl	54.54% <63.63%> (+2.37%)	⬆️
src/bandstructure.jl	81.79% <100.00%> (-0.15%)	⬇️
src/parametric.jl	77.89% <100.00%> (+0.23%)	⬆️

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