fix: declare packaging as an explicit dependency

[dimitri-yatsenko]

Summary

src/datajoint/migrate.py imports from packaging.version import Version, but packaging is not declared 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'

Pre-existing bug — reproduces on 2.2.2 and 2.2.3 — but became user-visible with Python 3.12's leaner venvs.

Reproducer

python3.12 -m venv /tmp/dj-test
/tmp/dj-test/bin/pip install datajoint==2.2.3
/tmp/dj-test/bin/python -c "import datajoint as dj; print(dj.__version__)"
# ModuleNotFoundError: No module named 'packaging'

Fix

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

Release target

Candidate for 2.2.4 (patch fixing a real import datajoint regression in clean Python 3.12 venvs).

Test plan

• Reproduce the failure on 2.2.3 in a clean Python 3.12 venv
• After this PR's wheel is built: confirm import datajoint succeeds in the same reproducer
• Pre-commit hooks pass