v0.18.20241020: rolling release (first 3.9 only release)

What's Changed

• general: 3.8 reached EOL, remove legacy code and make pytz optional dependency by @karlicoss in #70
• marshall.cachew: better exception in case we fail to get type hints from type by @karlicoss in #71

Full Changelog: v0.17.20241017...v0.18.20241020