[FIX] Issue 128: unregister TwinModel.__del__ from atexit and enhance PR116

[chrpetre]

Multiple enhancements to Fix #128:

• Remove registration of TwinModel.del() to atexit module which was preventing garbage collector to call it at the end of a loop (see Issue TwinModel instance keep allocating memory when used in a loop #128 details), remove the TwinModel.del() method
• Modify current logic to prevent issue with settings module trying to delete pytwin process temporary folder while some TwinRuntime objects have not closed their log file stored in the model directory. To do that, let TwinModel manages its model directory deletion and ensures its TwinRuntime log file has been released before deleting its model folder. This provides a cleaner fix to Issue [FIX] Register __del__ method of TwinModel to avoid issue atexit #116
• Add an explicit close method to TwinModel.

[codecov-commenter]

Codecov Report

Merging #134 (c3c791b) into main (b4fe3d3) will increase coverage by 0.09%.
The diff coverage is 72.22%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #134      +/-   ##
==========================================
+ Coverage   88.68%   88.77%   +0.09%     
==========================================
  Files          11       11              
  Lines        2350     2360      +10     
==========================================
+ Hits         2084     2095      +11     
+ Misses        266      265       -1     

[chrpetre]

@lboucin all tests are now green, ready to review

[lboucin]

LGTM. Thanks @chrpetre