Isolate solv::ObjQueue

[AntoinePrv]

Part of #2302.

Here the Queue is isolated in a safe RAII object.
It was made to use std conventions rather than libsolv ones.

This is private API so does not have any consequence.

On the immediate side, it caught some memory leaks in MSolver!

[Hind-M]

Nice!
A slight nitpicking, new files should have 2023 instead of 2019 or 2022 in the license section for history consistency.

[wolfv]

Looks very good to me!

I was wondering about the header location (solv-cpp/queue.hpp vs something like mamba/internal/solv-cpp/queue.hpp). But I guess it doesn't matter much since we're not installing that header, right?

And the rest was just some tiny comments.

[AntoinePrv]

@wolfv Yes these headers are private (hence the std::unique_ptr).
On the longer run we could make it its own implementation library, that is in CMake but never packaged or installed.
That would further ensure that we are keeping a strict separation of abstractions.

[Klaim]

Note that technically libmamba have more private headers, notably the ones in src/core/

[AntoinePrv]

They are not really private, they are installed, and needed by public headers.

[Klaim]

Side note that stylistically I would prefer default initialization to not have an assignation. I understand that it's valid in C++17, but it looks redundant and noisy to me when reading the code.
Weak "meh" here, to be clear.

[Klaim]

Use fmt here (maybe with a comment to use std::format once C++20 is available)

[AntoinePrv]

The idea is to keep these wrappers dependency free so I think we should avoid using fmt until there is some strong need for it.

[AntoinePrv]

Bad branch manipulation.