chore: use pip-compile for freezing dependencies

[gruyaume]

Description

use pip-compile for freezing dependencies and move all test dependencies from deps in tox.ini to the test-requirements.in file (instead of having our dependencies represented in 2 different ways).

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that validate the behaviour of the software
• I validated that new and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules