feat: copy demos to tmp dir

[MeteorsLiu]

Resolves #480

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.35%. Comparing base (cab94cc) to head (cd139bb).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #482   +/-   ##
=======================================
  Coverage   84.35%   84.35%           
=======================================
  Files          27       27           
  Lines        2723     2723           
=======================================
  Hits         2297     2297           
  Misses        385      385           
  Partials       41       41           

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