fix: handle filtered updates in Neighborhoods properly

[triceo]

If filters are in play, we can get an update even without seeing an insert first.
The code needs to account for this, just like it does in CS.

Also improves the move stream factory API following up on feedback.

[Copilot]

Pull request overview

This PR updates the Neighborhoods (preview) move stream APIs and internals to better handle updates/retracts when tuples are filtered, and consolidates related tests.

Changes:

• Consolidates neighborhood-related tests into a new NeighborhoodsTest.
• Extends MoveStreamFactory with new list-variable enumeration methods and updates ListChangeMoveProvider to use the new API.
• Adjusts enumerating dataset instances and DefaultMoveStreamFactory logic to better support filtered tuple lifecycles and new list-variable destination enumeration.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
core/src/test/java/ai/timefold/solver/core/impl/neighborhood/NeighborhoodsTest.java	New consolidated test coverage for local search, null handling, and notifications.
core/src/test/java/ai/timefold/solver/core/impl/neighborhood/NeighborhoodsNotificationTest.java	Removed; coverage moved into NeighborhoodsTest.
core/src/test/java/ai/timefold/solver/core/impl/neighborhood/NeighborhoodsBasedLocalSearchTest.java	Removed; coverage moved into NeighborhoodsTest.
core/src/main/java/ai/timefold/solver/core/preview/api/neighborhood/stream/MoveStreamFactory.java	Adds new public preview API methods for list-variable enumeration and deprecates older method.
core/src/main/java/ai/timefold/solver/core/preview/api/move/builtin/ListChangeMoveProvider.java	Switches to the new destination enumeration API.
core/src/main/java/ai/timefold/solver/core/impl/neighborhood/stream/enumerating/common/AbstractRightDatasetInstance.java	Adds fail-fast checks and changes update/retract behavior for filtered tuple scenarios.
core/src/main/java/ai/timefold/solver/core/impl/neighborhood/stream/enumerating/common/AbstractLeftDatasetInstance.java	Adds fail-fast checks and changes update/retract behavior for filtered tuple scenarios.
core/src/main/java/ai/timefold/solver/core/impl/neighborhood/stream/DefaultMoveStreamFactory.java	Implements the new API methods and refactors list-variable destination/assigned-value enumeration.

[sonarqubecloud]

Quality Gate failed

Failed conditions
59.7% Coverage on New Code (required ≥ 70%)

See analysis details on SonarQube Cloud