Backwards incompatible changes for Timefold Solver 2.0.0 (unplanned)

[triceo]

We use this issue to remind ourselves of what we need to do (or might want to do) when the time for Solver 2.0 comes.

Backwards Compatible breaking ideas:

• [ ] Remove all deprecated APIs
• [ ] Move LookUpStrategyType and PlanningId from package "domain.lookup" to package "domain.common"
• [ ] Remove "quarkus." prefix of "quarkus.timefold..." application.properties?
• [ ] Create an API JAR separate from the core JAR.
• [ ] An @PlanningEntityCollectionProperty on List<Object> getEntities(), List<String> or List<ShadowEntity> should fail fast?
• [ ] Extend the SolverStatus enum to the following values: NOT_SOLVING, SOLVING_SCHEDULED, SOLVING_ACTIVE, SOLVING_COMPLETED, SOLVING_FAILED;
• [ ] Better name for NearbyDistanceMeter? Doesn't only measure distance, also travel time etc.
• [ ] Input validation for constraint names; prevent crazy things like weird whitespace etc.
• [ ] Find and remove all uses of Serializable, EventObject and other lesser known JDK APIs which seem out of place in 2025.

[ge0ffrey]