adaptive: use std::unique_ptr and auto when possible

Draft because depends it might depends on !1615 (merged), and I still have a few things to check.

It uses auto to simplify the iterator type, easing the transition from vector<Segment*>::iterator to vector<unique_ptr<T>>::iterator, while also removing iterators from the loops.

It then change the vector to use unique_ptr, making a clear ownership signal and ensuring there is no leaks of segments.

Note that among the auto use, it uses auto as a lambda parameter which is C++14.