ENH: Adopt PEP 396: make the __version__ property available

[jhlegarreta]

Adopt PEP 396: make the __version__ property available to the package.

Documentation:
https://peps.python.org/pep-0396/

[jhlegarreta]

Although the error may be fair, not sure why the nibabel version comes into play now:
https://github.com/scil-vital/tractolearn/actions/runs/4125659552/jobs/7126514429#step:6:22
https://github.com/scil-vital/tractolearn/blob/main/pyproject.toml#L41

An option would be to try to use nibabel==3.0.0 and to remove manually installing 3.2.1 if we do not need newer features.

Another alternative to get the version hoping it will not try to look at versions of third-party packages:

import os
import re

dir_path = os.path.dirname(os.path.realpath(__file__))
with open(os.path.join(dir_path, "_version.py")) as f:
    s = f.read()
m = re.search("version =(.+?)\n", s)
if m:
    found = m.group(1)
__version__ = found.replace("\'", "")

Yet another alternative:

from ._version import version as __version__