Force svg+xml for GraphViz object as a workaround

[bvdmitri]

@FraserP117 gave me this idea in our private conversation and it actually worked pretty neatly!

Reference https://docs.julialang.org/en/v1/base/io-network/#Multimedia-I/O

The implementation wraps the GraphViz object in a "wrapper" that does only "support" svg and text display formats.
So now if display supports svg it will automatically show the svg image, otherwise it fallbacks to the dot strings as @FraserP117 planned originally. e.g compare:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.64%. Comparing base (bbb6781) to head (ddd1dd8).
Report is 4 commits behind head on main.

Additional details and impacted files

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##             main     #268   +/-   ##
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  Coverage   90.64%   90.64%           
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  Files          16       16           
  Lines        2170     2170           
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  Hits         1967     1967           
  Misses        203      203           

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[bvdmitri]

Lets wait for @FraserP117 input before merging

[FraserP117]

I'm reviewing/testing locally now. Apologies for the delay!

[jhlq]

This is a good workaround until the GraphViz package can be updated from the deprecated Cstring vector representation. I did ]dev GraphViz and changed the lines

const julia_cairo_name = Vector{UInt8}("julia:cairo")
const julia_cairo_libname = Vector{UInt8}("julia:cairo")

in src/cairo.jl to

const julia_cairo_name = Base.unsafe_convert(Cstring,"julia:cairo")
const julia_cairo_libname = Base.unsafe_convert(Cstring,"julia:cairo")

and that seems to fix the render bug.

[FraserP117]

Very nice stuff @bvdmitri. I have tested this locally in VSCodium and Jupyter notebook. Both work quite well.

When using Jupyter notebook, I do seem to get an error relating to the Cairo.jl renderer being unavailable - see the enclosed screenshots.

We could hold it up and investigate further but I favour passing this PR and improving from there. Perhaps we can implement the fix that @jhlq used above - in the form of a PR to Cairo.jl?

[bvdmitri]

I think Cairo.jl is fine, the problem is with GraphViz.jl, I opened several issues there but didn't get any response (except for @jhlq). I also couldn't run tests for GraphViz.jl locally. I do encourage you to open a PR to their codebase though @jhlq @FraserP117