chore: Change class and decorators locations to match new layout

[Christopher-Chianelli]

• In general, ai.timefold.solver.core.api.x and its subpackages -> timefold.solver.x.

• Exception for ai.timefold.solver.core.api.solver, which it and its subpackages -> timefold.solver.

• ai.timefold.solver.core.x and its subpackages -> timefold.solver.x (test and config).

• Use dynamic all when not TYPE_CHECKING for score and domain, since they have some classes that require the JVM to be started When TYPE_CHECKING, there are stub classes that the TYPE_CHECKER will see.

• Remove @incremental_score_calculator decorator, since it been replaced by IncrementalScoreCalculator ABC.

• Create an empty Constraint stub so users can reference it in their type signatures without importing something from Java.

[Christopher-Chianelli]

Where should nearby_distance_meter go (which is inside an impl.heuristic.selector)? I currently have it with the domain classes; probably should be moved to timefold.solver.heuristic?

[Christopher-Chianelli]

Enterprise PR: https://github.com/TimefoldAI/timefold-solver-python-enterprise/pull/3