Add non-copyable type support in std::vector binding

[jorisv]

There is no way to bind a std::vector with non copyable type (list std::unique_ptr).

[ManifoldFR]

Coming back to this issue

The problem is with Boost.Python rather limited indexing_suite, which defines __getitem__, etc, methods without allowing the user to inject a return policy:
https://github.com/boostorg/python/blob/0474de0f6cc9c6e7230aeb7164af2f7e4ccf74bf/include/boost/python/suite/indexing/indexing_suite.hpp#L174-L190

What's uncertain right now, is if a subclass of boost::python::indexing_suite can redefine these methods safely at the extension point template<class Class> extension_def(Class &cl) provided by the derived class DerivedPolicies in the CRTP.