Closing the stdout file descriptor when finished

[esheder]

Description

Currently, since the _run function in the executor.py file uses the stdout of the Popen it creates, it can sometimes fail to close that resource when the process is finished, leading to a ResourceWarning: unclosed file <_io.TextIOWrapper ...> warning.
This happened to me consistently when plotting a specific model, but does not happen for all the models I try to plot. However, Python's tracemalloc option points to this particular file descriptor being left open on those rare cases, and this fix stopped the warnings on my end.

I don't think it hurts to release this resource explicitly when the process is finished and we break from the printing loop, so this is a case of a small cost in terms of lines of code for a small benefit in terms of unintended warnings.

Checklist

• I have performed a self-review of my own code
• I changed no C++ source files, so I did not have to run clang-format (version 18)
• I have followed the style guidelines for Python source files (if applicable)
• There were no corresponding changes to be made to the documentation
• I have added tests that prove my fix is effective or that my feature works (if applicable)

If adding a test for this case is required, I can try to find a minimal working example of this warning case.

[paulromano]

Makes sense; thanks @esheder!