heyoka 4.0.3

This is a quick release that fixes a couple of build issues, one on FreeBSD and the other affecting the unit tests when building with GCC 13.

NOTE: heyoka 4.x introduces several breaking changes with respect to the 3.x series. Please see the following link for a list of breaking changes and explanations on how to adapt your code to the new API:

https://bluescarni.github.io/heyoka/breaking_changes.html#bchanges-4-0-0