Incompatibility with Python 3.12

[encukou]

Python 3.12 changes the internal representation of int objects (to speed up common cases). Usage of Py_SIZE and ob_digit in convert.pyx will fail.

The supported way of extracting the value of integers (if they don't fit in a C long long) is the Python method to_bytes, and there's from_bytes to go back. (If this is too slow for cypari, please chime in in the discussion.)

(edit) See also: python/cpython#101292

[tornaria]

Could we use _PyLong_FromByteArray and _PyLong_AsByteArray ?

[tornaria]

I think those will be hard to use because pari/gmp stores integers in "word little-endian" meaning [word0, word1, word2, ...]. This is the same as byte little-endian when the words themselves are little-endian. But in a big-endian architecture, there's no natural way to do it.