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?

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

♻️ 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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[coveralls]

coverage: 98.474% (+0.009%) from 98.465% when pulling c865f58 on feat/deprecate-unquoted-windows-paths into c1784c4 on main.