chore(deps,tooling,ci): replace pyspelling with codespell in tox

[danceratopz]

🗒️ Description

Use codespell instead of pyspelling in the spellcheck tox environment.

Benefits over pyspelling:

1. Catches more errors; checks filenames.
2. Doesn't require a word list (whitelist.txt).
3. Automated fixes: Single-suggestion spelling errors can be fixed with --write-changes
4. Fast execution: No external dependencies like aspell required

whitelist.txt is kept for now, it's still used by the VS Code cspell extension.

🔗 Related Issues

Fixes #811

• chore: replace flake8, flake8-spellcheck, isort and black with ruff and codespell #811

✅ Checklist

• All: Set appropriate labels for the changes.
• All: Considered squashing commits to improve commit history.
• All: Added an entry to CHANGELOG.md.
• All: Considered updating the online docs in the ./docs/ directory.

[marioevz]

LGTM, thanks!