Standardise Python to language agnostic errors

[kieran-ryan]

🤔 What's changed?

• Consolidate Python error messages to standardised format

<TBD>

⚡️ What's your motivation?

• Closes Python: Make tests pass against shared test data #18

🏷️ What kind of change is this?

• 🏦 Refactoring/debt/DX (improvement to code design, tooling, etc. without changing behaviour)

♻️ Anything particular you want feedback on?

• At present, it appears this will affect some unit tests within behave matching these error messages - with behave pinning cucumber-tag-expressions >= 4.1.0
• Whether consider any regressions within error messages
• Whether appropriate to align these errors with other implementations - given the reason listed against the error messages: "TOO MANY DIFFERENCES: Error message here are more specific (IMHO)"
• Guidance/direction - what is appropriate way to resolve - interested in all perspectives
• Points of extension within Behave - for awareness

📋 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.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

[kieran-ryan]

Pending small optimisations following redactions, some further exploratory testing, cleaning up the PR description; properly evaluating compatibility with points of extension by Behave; and ultimately agreement on whether aligning with this format is something we should proceed with (particularly if any error messages considered a regression) or whether we should look to enhance messages (or even a subset) alongside.