Fix: delete URL object after use in URL demo JS code

[rmisev]

See: https://emscripten.org/docs/porting/connecting_cpp_and_javascript/embind.html#memory-management

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.66%. Comparing base (60d7c0e) to head (a3b9e2c).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #102   +/-   ##
=======================================
  Coverage   99.66%   99.66%           
=======================================
  Files          16       16           
  Lines        2679     2679           
  Branches      432      432           
=======================================
  Hits         2670     2670           
  Misses          9        9           

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