docs: Use new Quantinuum docs theme

[mark-koch]

Closes #368

Based on https://github.com/CQCL/hugr/pull/1267

Page artifact can be downloaded here: https://github.com/CQCL/guppylang/actions/runs/11127889369/artifacts/2001389346

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.39%. Comparing base (9cbb917) to head (6c3b03e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #519   +/-   ##
=======================================
  Coverage   91.39%   91.39%           
=======================================
  Files          59       59           
  Lines        6481     6481           
=======================================
  Hits         5923     5923           
  Misses        558      558           

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[CalMacCQ]

now done in #1031

[mark-koch]

Closed by #1031