Thread leak after terminating a SolverJob

The SolverManager delegates disposing of consumer threads to the SolverJob.close() method, as the SolverJob owns the consumer thread.

However, when a Solver terminates, the SolverJob is deregistered from the SolverManager and, as a result, SolverManager.close() does not call SolverJob.close() to properly dispose of the consumer thread.

Even if the SolverJob.close() was called from the SolverManager.close(), the SolverManager may run over a long period of time and the number of consumer threads would still grow. The `SolverJob.close()` must be called also right after the last best solution is consumed.