fhlasek/fixgraph: refactor of graph/ to follow the linter style

[fhlasek]

Description of Change

Continuation of #954 and #983. Addresses #932.

Checklist

• Added description of change
• Added tests and example, test must pass
• Added documentation so that the program is self-explanatory and educational - Doxygen guidelines
• Relevant documentation/comments is changed or added
• Search previous suggestions before making a new one, as yours may be a duplicate.
• I acknowledge that all my contributions will be made under the project's license.

[Panquesito7]

Please, pick one file at a time, not more than five.
We will do much better job improving file by file.

Thank you.

[Panquesito7]

Sounds good to me. We can merge this to enable CI and continue
improving the code and adding documentation in another PR. 👍

[fhlasek]

@Panquesito7 @kvedala @ayaankhan98 do you want me to continue splitting files one by one or do you think it's manageable at the current size?

[kvedala]

@Panquesito7 @kvedala @ayaankhan98 do you want me to continue splitting files one by one or do you think it's manageable at the current size?

Maybe we can split a couple of more files, so that this repo contains a single digit of modified files? Thank you @fhlasek

[kvedala]

👍 Looks good otherwise
Great work, @fhlasek

[Panquesito7]

LGTM. 👍

[ayaankhan98]

great work @fhlasek
Thanks for your contribution!