fix: in event consumption, always release the lock if we already aquired it

[triceo]

Cherry-pick of 5065095

[Copilot]

Pull request overview

This PR fixes a concurrency bug in the Timefold Solver's event consumption mechanism where semaphore locks (used to order solver events) were not always properly released. The fix moves lock release logic into whenComplete/whenCompleteAsync callbacks on CompletableFuture, ensuring locks are released even when exceptions occur. Additionally, mutable fields accessed across threads are converted to AtomicReference for proper thread safety, and a timeout is added to terminateEarly() to prevent indefinite blocking.

Changes:

• Refactored ConsumerSupport to release semaphores in whenComplete callbacks instead of finally blocks inside async tasks, ensuring lock release even on exceptional paths.
• Converted DefaultSolverJob fields (solverStatus, finalBestSolutionFuture, consumerSupport) from volatile/plain fields to AtomicReference for proper thread-safe access.
• Added a 1-minute timeout to terminateEarly() with escalation logic to prevent indefinite blocking.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
core/src/main/java/ai/timefold/solver/core/impl/solver/DefaultSolverJob.java	Converted fields to AtomicReference, extracted terminateEarlyLocked() with timeout and idempotency, added null-safety checks
core/src/main/java/ai/timefold/solver/core/impl/solver/ConsumerSupport.java	Moved semaphore releases to whenComplete callbacks, added @NullMarked, added class-level Javadoc, refactored to return CompletableFuture for chaining
core/src/main/java/ai/timefold/solver/core/impl/solver/BestSolutionHolder.java	Removed redundant @NonNull annotation (class is already @NullMarked)
core/src/main/java/ai/timefold/solver/core/api/solver/SolverJob.java	Updated Javadoc for terminateEarly() to document the new timeout behavior