Narwhals v0.9.9

Changes

✨ Enhancements

• enh: .head() and .tail() (#297)
• enh: dataframe and series .item() (#296)

📖 Documentation

• clean: format docstrings with ruff (#294)
• docs: Contributing steps update (#293)

🛠️ Other improvements

• test: nox for local testing (#295)

Thank you to all our contributors for making this release possible!
@DeaMariaLeon, @FBruzzesi and @MarcoGorelli