Drop python 2 compatibility

[youtux]

🤔 What's changed?

Dropped python 2 compatibility.

⚡️ What's your motivation?

I want to improve the python codebase, initially adding type annotations. But the python2 compatibility code makes it harder, so since python2 was EOL'd 4 years ago, I'd propose to remove supporting it.

Users needing python2 can still use older versions of the package.

🏷️ What kind of change is this?

• 🏦 Refactoring/debt/DX (improvement to code design, tooling, etc. without changing behaviour)
• 💥 Breaking change (incompatible changes to the API)

♻️ Anything particular you want feedback on?

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

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[jsa34]

https://github.com/cucumber/gherkin/blob/main/.github/workflows/test-python.yml needs updating to remove py2 from the matrix

[jsa34]

Looks good to me.
We will resolve the Windows encoding issue separately.