Improve Python module testing and cleanup memory leaks

[jabraham17]

Make more of the Python package module tests run more frequently. While doing this, I also cleaned up as many of the Python memory leaks in the Python module as I could find.

Some of the tests rely on external Python dependencies like torch and numba. Previously, these tests were always skipped and a "compileOnly" version was tested. This PR adds a step to the skipif to install the dependencies locally if they are missing. This allows the tests to actually be executed in more cases

This PR also adds support for checking for unfree'ed references, controlled by the --pyMemLeaks flag. This relies on an external python dependency, so this uses similar external Python dependencies testing support as above

Testing

• start_test test/library/packages/Python
• start_test -memleaks test/library/packages/Python

Future Work:

• remove global toFree list

[Reviewed by @DanilaFe]

[DanilaFe]

Looks good generally, per our conversation the CLEARs might need a revisit in future PRs.

[bradcray]

@jabraham17 : Would I/we want to (and be able to) leverage the work here in the Chapel 2.3 blog release announcement to test more of the GPU code? IIRC, we disabled the testing of the first example due to its use of PyTorch?

[jabraham17]

Very much so, all that should be required is to copy over a few test files like the pytorch .skipif, skipIfAndInstallPackage.sh, and the improved EXECENV. Nothing else should need to change