Unless I've misunderstood this API, and the `ByteArray` part doesn't refer to an array of bytes representing the value of `PyLong` in 2's complement, can we implement this in the public header? It's already available, it's just not exported (at least I can't use it, and it's not in the documentation). This would be beneficial for fixed width integer types, especially ones larger than `long long` (e.g. `__int128_t`), and shouldn't take much effort since it's already implemented privately (https://github.com/python/cpython/blob/04fc4f2a46b2fd083639deb872c3a3037fdb4...). Possibly include a function to return the size of the would-be array to be used as a check? Also since I have nowhere else to ask it, what's with `PyLong_AsSignedType` doing type coercion for you, but `PyLong_AsUnsignedType` not? (At least that's what I gathered from the documentation)