New container in Boost.PolyCollection, additions to Boost.Mp11 and more

https://cppalliance.org/joaquin/2025/01/05/Joaquins2024Q4Update.html

CI support added for several Boost libraries; a boost::variant_collection groups same‑type elements; Boost.Mp11 adds mp_lambda and faster mp_is_set; documentation URLs modernized; sponsorship work done.