Missing the __version__ attribute

[BDonnot]

I think, if possible, the __version__ attribute should be exported in the main package, for example in the file pypowsybl2grid/__init__.py :

# Copyright (c) 2024, RTE (http://www.rte-france.com)
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.
# SPDX-License-Identifier: MPL-2.0

from .pypowsybl_backend import PyPowSyBlBackend
from .util import write_obs_json
__version__ = "0.1.0"

[BDonnot]

(I can do a PR if you prefer)