Support latest Python and typing-extensions.

What's Changed

• Add benchmark for apischema by @wyfo in #192
• Switch to poetry-core by @fabaff in #193
• Update typing-extensions, plus a fixes for other breaking changes. by @seandstewart in #203

New Contributors

• @wyfo made their first contribution in #192
• @fabaff made their first contribution in #193

Full Changelog: v2.8.0...v2.8.1