Sanitise docs

[Yaswant Pradhan (yaswant)]

** DONT MERGE **

This PR is replaced by #427

Revisited various technical debts going through the entire documentation. No major changes to to contents.

Change summary

• Update README.md with Simulation Systems repositories diagram (on GitHub); happy to move this to repo Wiki
• Introduce pyproject.toml and uv to manage package dependencies
  • Note: I've updated .github/workflow/requirements.txt file, in case someone still wants to use conda (for this project I'd argue against it though). In principle, both env.yml and requirements.txt files can be safely deleted.
• Introduce sphinx-lint to check restructured text (pyproject.toml)
• Add some exceptions for link check (conf.py)
• Replace pip with uv in GitHub Actions
• Reformat almost all rst files
  • for consistent column width
  • fix some syntax errors
  • remove hidden Unicode characters (U+200B zero widh space) injected from someone's editor which made it impossible to compile latexpdf.

[Yaswant Pradhan (yaswant)]

superseded by #427