Enable coverage in CI (#992)
* some tests
* add pytest-cov package
* another ci test
* new test - and quicker
* new test ?
* maybe coverage everywhere :)
* upload coverage in CI
* refacto tests in single matrix
* force ci
* fix workflow
* fix again
* set fail fast to false
* FIX tensorflow tests
* enable codecov comment on PRs
* remove unused CI parameter + add badges to readme
