fix: declare packaging as an explicit dependency

src/datajoint/migrate.py imports ``packaging.version.Version`` but
``packaging`` is not listed in pyproject.toml dependencies. None of the
declared deps pull it in transitively, so a fresh ``pip install datajoint``
into a clean Python 3.12+ venv (where the venv no longer ships setuptools
by default) leaves ``packaging`` uninstalled and ``import datajoint``
raises::

    ModuleNotFoundError: No module named 'packaging'

This is a pre-existing bug — same failure reproduces on 2.2.2 and 2.2.3
— but only became user-visible with Python 3.12's leaner venvs.

Adds ``packaging`` to the dependencies list. No version pin since
``migrate.py`` uses only the basic ``Version`` class, which has been
stable across the package's history.

Author: dimitri-yatsenko

pyproject.toml

@@ -16,6 +16,7 @@ dependencies = [
   "pydot",
   "fsspec>=2023.1.0",
   "pydantic-settings>=2.0.0",
+  "packaging",
 ]
 
 requires-python = ">=3.10,<3.14"