allow single-item arrays as a format

[davidjgoss]

🤔 What's changed?

When expressing a format as an array, support a single-item array in the typing.

⚡️ What's your motivation?

If you want to use a formatter for stdout but with a local path containing colons etc, you may want to express that as a single item array to avoid Cucumber seeing the colon(s) and interpreting it as a formatter+target string to be broken apart. See https://github.com/webdriverio/webdriverio/pull/11010/files#r1309127113 for an example in the wild.

This worked anyway at runtime, but the types needed to reflect that, and some tests have been updated to prove it.

🏷️ What kind of change is this?

• 🐛 Bug fix (non-breaking change which fixes a defect)

📋 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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