Release version 2.0

This MR aims at finalizing the package to proceed with its public release, as a clean 2.0 version.

Release To-Do List

Must have

Polish up the code:

• add ClassVar type annotations to class attributes
• add NoReturn type annotations to exception-raising functions (if any)
• clean up __init_subclass__ implementations see docs
• verify module docstrings;
• verify __all__ statements
• garbage-collect unused statements in abstract methods
• garbage-collect deprecated Model.compute_loss method
• implement pending hotfixes (notably to Readme and Vector classes)

Add required metadata:

• add LICENSE file
• add license-related header in all code files
• add AUTHORS file
• update package version (use a VERSION file?)

Test the package extensively:

• run tox with python [3.8, 3.9, 3.10, 3.11]
• drop support for python 3.7*

*Support for python 3.7 was dropped due to functions such as typing.get_args and typing.get_origin having been introduced with Python 3.8.

Could have

Improve dependency specifications:

• update dependencies' versions (possibly running tests, e.g. for TF)
• update black version (~=23.0)
• revise version requirements for pylint and mypy (current are OK and CI/CD uses the latest anyway)

Add more unit tests:

• units tests for Vector (see MR !22 (merged))

Add coverage stats:

• compute (and report in some sort) tests' coverage

Unplanned additions

• Modularize tests execution to be resilient to tensorflow and/or torch not being available.