Fix incorrect binding language detection and prioritization for Visual Studio extension

[Copilot]

🤔 What's changed?

• Fixed incorrect binding language detection when reading reqnroll.json
• Ensured language.binding takes priority over legacy bindingCulture format
• Added comprehensive unit tests

⚡️ What's your motivation?

Setting the binding culture in reqnroll.json had two issues:

1. It incorrectly set the feature language instead of the binding language
2. The legacy bindingCulture format took priority over the newer language.binding format

User configuration that triggers the bug:

{
  "language": {
    "binding": "fr-FR"
  },
  "bindingCulture": {
    "name": "de-DE"
  }
}

Expected behavior:

• Feature files remain in English
• Step argument conversion uses French culture (fr-FR) for dates/numbers
• New language.binding format should take priority over legacy bindingCulture

Actual behavior before fix:

• Feature language got set to French, breaking English feature file parsing in Visual Studio
• Legacy bindingCulture overwrote language.binding setting

Fixes #102

🏷️ What kind of change is this?

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

📋 Checklist:

• 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 "[vNext]" section of the CHANGELOG, linking to this pull request & included my GitHub handle to the release contributors list.

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[clrudolphi]

LGTM

All done

[gasparnagy]

Released in https://github.com/reqnroll/Reqnroll.VisualStudio/releases/tag/v2025.2.359