warn for ambiguous colons in formats

[davidjgoss]

🤔 What's changed?

Emit a warning with a link to deprecation docs when formats are specified with ambiguous colons.

⚡️ What's your motivation?

We have some smart handling for things like file:// URLs for now, but I'd rather not maintain this forever and instead have users just quote the parts of the format string (or use the array notation, in a config file), at which point we can reduce our complexity.

🏷️ What kind of change is this?

• :bank: Refactoring/debt/DX (improvement to code design, tooling, documentation etc. without changing behaviour)
• :zap: New feature (non-breaking change which adds new behaviour)

♻️ Anything particular you want feedback on?

📋 Checklist:

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

---

This text was originally generated from a template, then edited by hand. You can modify the template here.

[coveralls]

coverage: 98.474% (+0.009%) from 98.465% when pulling c865f5867b26cf2594cac6a588d3324a85dd3241 on feat/deprecate-unquoted-windows-paths into c1784c46965e83227fd4f8632dc18fe0a2099c59 on main.