fix(Type): memory leak

[mcakircali]

replace raw ptr with unique_ptr
metkit::mars::Context::add and similar

[danovaro]

looks good to me

[pmaciel]

Note that there is a principle in this pattern, of passing pointers. The idea is if you pass a pointer you obviously tranfer the responsibility to manage it, hence tranfer ownership. Hence smart pointers aren't useful -- here, to replace the idom.

Now, maybe the function/method name itself isn't clear as it isn't "makeSomething" but when returning a pointer is an indication that it is a polymorphic type, and you don't loose type information this way either.

It is a pattern I didn't agree initially but learnt to be useful. It will be found in many places: eckit, atlas, mir, pgen, metview, mars-client (the classic one) and likely others. If we are to rewrite this, it is a massive change everywhere...