Add a structurally_biorthogonal check for star bicoloring

[amontoison]

• Fix three typos (symmetrix and matric).
• Add a function proper_length_bicoloring to check the length of the two color vectors returned by a bicoloring.
• Add a function structurally_biorthogonal based on a "new" definition of star bicoloring.

I don't know if a star bicoloring on A was already defined like this before but it’s something we could easily derive from the definition of a symmetric star coloring on [0 A'; A 0].

I verified this definition of star bicoloring on the problems rectangle and arrowhead.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (0246517) to head (e186a71).
Report is 3 commits behind head on main.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files           13        13           
  Lines         1257      1342   +85     
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+ Hits          1257      1342   +85     

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[gdalle]

well done!