doc: Modernize segment library examples and documentation

[Abhi-d-gr8]

Superseding #20.

Changes:

• Rebases the original improvements by @wenzeslaus onto the current main branch.
• Resolves all merge conflicts in lib/segment/segmentlib.dox, open.c, and get_row.c.
• Converts the documentation for the new example modules (r.example.segment and r.example.segmulti) from HTML to Markdown to match current GRASS GIS standards.
  Reference:
• Original PR: man: Improve segment library documentation, provide examples #20
• Fixes the request for Markdown conversion and conflict resolution.

[github-actions]

[pre-commit] _{reported by reviewdog 🐶}

grass/doc/raster/r.example.segment/r.example.segment.md

Line 32 in 3f785fa

[github-actions]

[pre-commit] _{reported by reviewdog 🐶}

grass/doc/raster/r.example.segmulti/r.example.segmulti.md

Line 41 in 3f785fa

[wenzeslaus]

We now use also CMake and I think the examples are compiled somewhere in the CI.

[Abhi-d-gr8]

Thanks for the feedback, @wenzeslaus ! I've now added CMake support for these examples and verified that they compile correctly. I also fixed the end-of-file newlines that the bot flagged.

[wenzeslaus]

This should not compile always, at the same time it needs to compile in the CI with the other examples.

While I appreciate the old PR cleanup, this needs more in depth work. If one AI run were enough, I would have merged that already.