fix: More accurate type hints for Python @planning_entity

[luxaritas]

Resolves #1265

[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.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
77.8% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Christopher-Chianelli]

LGTM, although the same change probably should be done for planning_solution (since that another decorator that has optional parameters); I can do that change myself. Unfortunately even with these changes, this won't do anything for PyCharm Intelisense (all lambda parameters are treated as Any in PyCharm in its custom type resolver; see this PyCharm issue for details).

[triceo]

Thank you for the contribution, @luxaritas!
The next release is coming up next week.