[Setup] Update setup to pyproject.toml

Context

Fix some issues with the pyproject.toml file.

Note that it allows also to use editable mode with : pip install -v --no-build-isolation -e .

Modified files

Modified:

• pyproject.toml:
  • fix package find/package_data to include aidge_export_cpp package without the unit_tests
  • remove useless build dependency on toml
  • add optional dependency on pytest
• aidge_export_cpp/__init__.py: use the newly generated _version.py file instead of the old version.txt file
• README.md: add install instructions

Removed:

• version.txt: replaced by _version.py

Detailed major modifications

No major modification

TODO

• Need to update dev branch from main first