Evaluate update to Nim 2.x

[gmega]

With gc:refc at first.

[2-towns]

I will create subtasks to ensure clear tracking of comments, as I believe we will have many comments.

[2-towns]

I updated constantine dependency to the last commit hash because there is a compilation error with Nim 2.X.

Additionally, I updated the PR created by Ben for GCC 14 on nim-poseidon2 to reflect this change.

[2-towns]

There is a problem with the default SAT resolver of nimble; it fails when trying to install dependencies; see vacp2p/nim-libp2p#1219.

I will use nimble --solver:legacy install until it is fixed.