fix: highlight_edge, highlight_path and highlight_vertex in 3D

[petercorke]

Highlighting on a 3D graph did not work in 1.0, although highlight_path did in 0.6.5. Found while checking that plotting is unchanged by the lazy-import change (#70): the 2D figures I rendered before and after were pixel-identical, but 3D highlight_path raised AttributeError: 'FancyArrowPatch' object has no attribute 'do_3d_projection' in both, so it predates that PR.

Cause

• highlight_edge passed the dimension 2 to _edge_artist whatever the axes were, so on a 3D graph a flat FancyArrowPatch was added to a 3D axes. Adding it succeeded; drawing the figure raised. highlight_path calls it. (This came in with the arrows in feat: plot() draws arrowheads, parallel edges and loops; clearer option names #51; 0.6.5 drew lines.)
• highlight_vertex used plt.plot(x, y), which on a 3D axes puts the marker at z = 0.

Fix

• The dimension is that of the axes: 3 if ax.name == "3d". So a 3D graph plotted with force_2d=True is highlighted in 2D.
• highlight_vertex plots [x], [y], [z] on a 3D axes.

Tests

There were none of highlighting in 3D. tests/test_highlight_3d.py draws the figure (that is where it failed) for both kinds of graph: an edge, a loop, a parallel edge, a path (checked for the artists it adds), a vertex (at its z) and several by name, a force_2d plot; and the 2D vertex marker and edge are unchanged.

771 tests pass, mypy clean. The eight figures I rendered for the comparison: the five 2D ones are pixel-identical to before, the 3D ones that failed now draw.

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[codacy-production]

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🟢 Metrics 18 complexity · 0 duplication

Metric	Results
Complexity	18
Duplication	0

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.54%. Comparing base (5fea937) to head (0e7e668).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #71      +/-   ##
==========================================
+ Coverage   97.28%   97.54%   +0.26%     
==========================================
  Files           4        4              
  Lines        1581     1586       +5     
==========================================
+ Hits         1538     1547       +9     
+ Misses         43       39       -4     

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