The sealed modifier was unnecessarily breaking inheritance for users who need
to extend CpSolver. The standard IDisposable pattern with protected virtual
Dispose(bool) allows safe inheritance while maintaining proper resource cleanup.
This change:
- Removes the sealed modifier from CpSolver class
- Implements the standard dispose pattern with protected virtual Dispose(bool)
- Allows derived classes to override disposal behavior safely
- Maintains backward compatibility for existing non-inheriting code
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