Update test suite

Changes to the code

• Rename all tests to the pytest standard naming convention
• Update to use pytest to run the tests and collect coverage
• Simplify gitlab CI script using above changes
• New ./coveragerc file to define which examples are omitted from the coverage
• New section in ./setup.cfg to explicitly show that we ignore the other_test.py[1]

Effect this will have

• The coverage report will not contain the path (see https://monash.docs.ligo.org/tupak/htmlcov/)
• The coverage will slightly increase, this is just due to using a different measurement
• The ./gitlab-ci.yml is noticeably easier to read and will be easier to modify in future

[1] This test is currently implicitly ignored by the CI (by not being called). Ultimately, we should remove this test or fix it, but I'm leaving that for another MR.