[Refactor] add .stream getter and deprecate toStream() extension

[jinyus]

Description

Replace the .toStream() extension method with a .stream getter. This is a bit more efficient since a map to cache the streams is no longer needed.

Type of Change

• [x] ✨ New feature (non-breaking change which adds functionality)
• [ ] 🛠️ Bug fix (non-breaking change which fixes an issue)
• [ ] ❌ Breaking change (fix or feature that would cause existing functionality to change)
• [x] 🧹 Code refactor
• [ ] ✅ Build configuration change
• [ ] 📝 Documentation
• [ ] 🗑️ Chore