PR: Replace pygraphviz with pydot.

[KelSolaar]

Summary

This PR replaces pygraphviz with pydot so that installation is easier: pygraphviz needs to be built whereas pydot is a pure Python package.

This simplifies the installation process tremendously by avoiding issues such as pygraphviz/pygraphviz#11

Preflight

Code Style and Quality

• Unit tests have been implemented and passed.
• Pyright static checking has been run and passed.
• Pre-commit hooks have been run and passed.
• [N/A] New transformations have been added to the Automatic Colour Conversion Graph.
• [N/A] New transformations have been exported to the relevant namespaces, e.g. colour, colour.models.

Documentation

• [N/A] New features are documented along with examples if relevant.
• [N/A] The documentation is Sphinx and numpydoc compliant.

[coveralls]

coverage: 99.835%. remained the same
when pulling b62105b on feature/pydot
into b83a73d on develop.