WIP: Using pytest instead of nose requires renaming to regression_test.py

[rjleveque]

After changing regression_tests.py to regression_test.py, using pytest seems to work fine.

It gave some warnings:

% pytest
=============================== warnings summary ===============================
../../../pyclaw/src/pyclaw/classic/solver.py:16
  /Users/rjl/git/clawpack/pyclaw/src/pyclaw/classic/solver.py:16: DeprecationWarning: the imp module is deprecated in favour of importlib and slated for removal in Python 3.12; see the module's documentation for alternative uses
    from imp import reload

classic/tests/acoustics_3d_heterogeneous/regression_test.py::Acoustics3DHeterogeneousTest::runTest
  <frozen importlib._bootstrap>:241: RuntimeWarning: numpy.ndarray size changed, may indicate binary incompatibility. Expected 16 from C header, got 96 from PyObject

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
======================== 1 passed, 2 warnings in 3.70s =========================

The first is fixed in clawpack/pyclaw#701.

I don't know what's up with the numpy warning.

@mandli, @ketch: We should discuss further before merging this to make sure pytest is what we want to use.

[ketch]

Answers here suggest that updating numpy may get rid of the second warning:

https://stackoverflow.com/questions/66060487/valueerror-numpy-ndarray-size-changed-may-indicate-binary-incompatibility-exp

I'm using numpy version 1.25.1 and I'm able to run the tests (using pytest) without getting that warning.

However, it should be noted that this still depends on nose (see line 32 of regression_test.py). If you uninstall nose, the tests won't run.

[rjleveque]

Thanks @ketch, but it does not look like the @wip is used anywhere so I tried to clean this up in
clawpack/clawutil#155

[rjleveque]

Merging this so we can test github CI