Export OSQP_info and OSQP_results in src/extension/src/osqpmodule.c

[litongyu]

Export these two types can make osqp pickleable, otherwise python cannot recognize these classes.

[Martin Stefanik]

Upvote for exporting OSQP_results and OSQP_info. This should be quick and it is helpful for code bases using type hints.