Is there any way to use the Context type. Perhaps we pass a Context object to a new method SolveInContext (but not just to Solve, which would violate the backward compatibility promise; the context package says Context objects should always be passed to every function that uses one rather than stored in a struct).

A user could not use picosat_set_interrupt more than once concurrently. We'll have to be careful to serialize access to it. Otherwise a timer going off (for example) for one Solve call would end all Solve calls. This may automatically be taken care of by way of Solve's use of a write lock.