Add the observable10 qualitative colormap

[apcamargo]

This PR adds the observable10 qualitative colormap from the Observable Plot library, as well as the observable namespace.

Example from the blog post introducing the palette:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.87%. Comparing base (6aecac5) to head (0d8eb11).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #67   +/-   ##
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  Coverage   96.86%   96.87%           
=======================================
  Files         154      155    +1     
  Lines        1980     1981    +1     
=======================================
+ Hits         1918     1919    +1     
  Misses         62       62           

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[tlambert03]

thanks!