Change docs theme to sphinx-book-theme

[benjeffery]

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[codecov]

Codecov Report

Merging #2197 (f50b225) into main (1963a68) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2197   +/-   ##
=======================================
  Coverage   91.46%   91.46%           
=======================================
  Files          20       20           
  Lines       11254    11254           
  Branches     2297     2297           
=======================================
  Hits        10293    10293           
  Misses        523      523           
  Partials      438      438           

Flag	Coverage Δ
C	91.46% <ø> (ø)
python	98.68% <ø> (ø)

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