Squashed commit of the following:

commit 687c4bb
Author: Tuoyuan Cheng <tycheng@nus.edu.sg>
Date:   Fri Aug 23 18:03:40 2024 +0800

    sampling order (tpl_sim) and vcp_from_sim (#25)

    * Update python-package.yml
    util.__init__ : ref_count_hfunc() to greedily find tpl_sim with min hfunc calls
    vinecop._data_vcp : one visit() for both hfunc and hinv in sim
    vinecop._factory_vcp: code refactoring to include the above

    * pyproject.toml, stdtr/stdtrit, README
    drop torch dependency for user customization

    * Update .yml
    pytest ./tests
    matrix.os

    * README, test_vinecop

    * sampling order, simplified