Make tests run against local code, fix syntax warning breaking coverage, and add code coverage generation to github actions

[scott-carroll-verses-ai]

• Update tests so they test against local code rather than the installed module
• Update syntax so the warning around ellipsis use doesn't break coverage generation
• Update github actions to produce a coverage report and attach it to the run

See:

• example run: https://github.com/scott-carroll-verses-ai/pymdp/actions/runs/9488505015
• example coverage artifact: https://github.com/scott-carroll-verses-ai/pymdp/actions/runs/9488505015/artifacts/1595277305

Related to issue #142