Add Graphviz Functionality to Nav for In-Tool Diagram Display

[alessandrocarminati]

The current version of nav requires users to pipe output to an external Graphviz tool like dot for generating diagrams images. This process can be time-consuming and inconvenient. Therefore, we request to incorporate Graphviz functionality within nav to allow users to generate diagrams images within the tool itself.

While the long-term goal is to create a web application for navigating code with diagram display, the objective is to maintain nav as a commandline tool. Users should be able to interact with diagrams using hyperlinks in the displayed source code.

[alessandrocarminati]

Check out these two branches

• https://github.com/AC-FuSa-Tools/nav/tree/ac-graphviz-integration
• https://github.com/AC-FuSa-Tools/nav/tree/ac-graphviz-integration_refactor

They've got the feature implementation Requested by this issue.
Plus, on the second branch, I'm suggesting a refactor of the sql component to abstract the persistence.
@mauriziopapini and I had a discussion about it and figured it could be pretty useful.