feat: Support deep_planning_clone class decorator

[luxaritas]

This brings parity with the Java version (I also found that DeepPlanningClone did not work on a planning solution ProblemFactCollectionProperty, whereas marking the entire class to deep clone does)

[triceo]

Thank you for your contribution, @luxaritas!

We are a bit short-handed at the moment, with many people already taking their year-end holidays. I'm going to leave this one open until my colleague, who owns the Python part of the codebase, comes back in early January and does a code review.

Please be patient - we have every intention to merge this PR.

[triceo]

On a general note though:

• Please make sure the existing test coverage passes. At the moment, it does not:

  py310: commands[0]> pytest --import-mode=importlib python/python-core/tests
  ImportError while loading conftest '/Users/runner/work/timefold-solver/timefold-solver/python/python-core/tests/conftest.py'.
  python/python-core/tests/conftest.py:1: in
  import timefold.solver
  .tox/py310/lib/python3.10/site-packages/timefold/solver/init.py:50: in
  import timefold.solver.domain as domain
  .tox/py310/lib/python3.10/site-packages/timefold/solver/domain/init.py:28: in
  from ._annotations import *
  .tox/py310/lib/python3.10/site-packages/timefold/solver/domain/_annotations.py:876: in
  def deep_planning_clone(entity_class: Type[A] = None) -> Type[A]: E NameError: name 'A' is not defined
  py310: exit 4 (0.21 seconds) /Users/runner/work/timefold-solver/timefold-solver> pytest --import-mode=importlib python/python-core/tests pid=3876

This issue also happens on Python 3.11 and 3.12. (We do not yet support 3.13.)

• Please introduce extra coverage for your change. There ought to be a test to check whether the deep-cloning works when declared.

[luxaritas]

Completely understand folks being out - I have my own local adjustments for my PRs so no big deal for me anyways!

I caught the CI failure after I'd already stepped away - copy-paste error. Will look into tests as well.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud