Fix stretch 0 random functions (#467)

* Add inf if scale 0 division

* Add tests

Remove get_html_theme_path

Update version

Add random functions tests and truncexpon (#441)

- Add random functions tests
- Fix truncation in Vensim's RANDOM NORMAL
- Support Vensim's RANDOM EXPONENTIAL

Fix initialization dependencies for Smooth

Support Python 3.12, numpy >= 1.24 and pytest 8.0.x. (#437)

* Support Python 3.12

* Support numpy >= 1.24

* Support pytest 8.0.x

* Avoid errors with DeprecationWarnings

* Custom error when netCDF4 is missing

Add support for XMILE's DELAY function

Fix bug with ModelOutput class

Add copy method

Drop support for Python 3.8 to use latests xarray versions