**Warning, this fix contains changes which will change the default behavior of core functions:**

* Default behavior of Optics is changed when AT lattice is loaded: now default to optic function to s=0 instead of average ones.
* Default behavior of LongRangeResistiveWall and ImpedanceModel when an AT lattice is loaded is to normalized by average_beta / local_beta
* Adds Optics.average_beta attribute
* Add pytest markers for tests and update .gitlab-ci.yml and pyproject.toml files.

+ run test suite and formatters when there is a merge request or commit on "stable" or "develop".
+ build docker image and pip package when a tag is pushed and commit on "develop".