Add the missing [Result.COMMIT] / [Result.CONFLICT] assertions so
that the two regression tests actually verify the expected conflict-set
outcome, not just that the calls do not crash.
ConflictSet_check, ConflictSet_addWrites, ConflictSet_setOldestVersion,
and ConflictSet_destroy return void in C, but the Python wrapper left
their ctypes restype at the default c_int. Set restype = None for each
to match the C API contract and avoid undefined behavior from reading
the return register of void functions.