Add test step to cibuildwheel.

[carlosperate]

Looking into adding tests (issue #19), and it looks like we can run a test step in cibuildwheel after each wheel is built, simple! 🥳
https://cibuildwheel.readthedocs.io/en/v2.16.2/options/#testing

So I've added pyusb as a test requirement and it runs python test.py.

• Is that the best current way to test the wheels?
• Is there something else this should do?

I was planning to add this as part of PR #20, but unfortunately the tests are failing on Linux, so I didn't want that to be a blocker for that PR.

This PR is running on top of the main branch without any other modifications, to test the current wheels, which I assume should be working.

Test result from my fork: https://github.com/carlosperate/libusb-package/actions/runs/6975861223/job/18983558875

Building cp37-manylinux_x86_64 wheel
CPython 3.7 manylinux x86_64
...
  Collecting pyusb
    Downloading pyusb-1.2.1-py3-none-any.whl (58 kB)
       ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 58.4/58.4 kB 4.8 MB/s eta 0:00:00
  Installing collected packages: pyusb
  Successfully installed pyusb-1.2.1
      + mkdir -p /tmp/tmp.G43sXfIgjj/test_cwd
      + sh -c 'python /project/test.py'
  Path to included library: /tmp/tmp.G43sXfIgjj/venv/lib/python3.7/site-packages/libusb_package/libusb-1.0.so
  Unable to load libusb backend!

libusb-package/test.py

Lines 13 to 17 in 7a62b64

	# Test find_library().
	libusb1_backend = usb.backend.libusb1.get_backend(find_library=libusb_package.find_library)
	if not libusb1_backend:
	print("Unable to load libusb backend!")
	sys.exit(1)

libusb-package/src/libusb_package/__init__.py

Lines 66 to 87 in 7a62b64

	def find_library(candidate: str) -> Optional[str]:
	"""@brief Look for a package resource starting with the provided candidate name.
	This function effectively implements the `find_library` callback used by pyusb's backends.
	However, it is general enough to be used for any code that needs a libusb library.
	@retval str Path to the contained library matching the candidate name.
	@retval None No library matching the candidate name is contained in libusb_package.
	"""
	lib_path = get_library_path()
	if not lib_path:
	# There is no library included in our installation, fall back to ctypes' find_library.
	return ctypes.util.find_library(candidate)
	lib_name = lib_path.name
	if lib_name.startswith(candidate) \
	or ((platform.system() == "Linux") and lib_name.startswith("lib" + candidate)):
	return str(lib_path)
	# We don't have a matching library.
	return None