BUG: API function calls do not cleanup correctly when a Python exception is thrown

[mdboom]

In driver, runtime and nvrtc, function calls may not clean up correctly if a Python exception is thrown during Python-to-C argument conversion.

Some argument types require cleanup upon exiting the function. For example, a Python sequence is serialized into a heap-allocated C array that must be free'd before exiting the function. Once the C array is allocated, an exception thrown by the conversion of a subsequence argument will cause the array to never be freed.

Traditionally in C, one would use a goto label to handle cleanup in complex, multi-argument functions. Since we use Cython, we can instead use try/finally. If a major performance impact is measured of that, we may need to use a cleanup helper function (which could be called from all exit paths) instead.