Fix failing JsonProvider tests by restoring original TwitterSample.json format

The PR changed TwitterSample.json from JSON Lines format (32 lines, 22 objects)
to JSON array format (1 line, 21 objects), breaking tests that expected:
- 22 total objects with SampleIsList=true
- 5 objects with null/empty/missing text fields
- 17 objects with actual text content

Restored the original JSON Lines format to fix the failing tests:
- 'Optional strings correctly handled when missing or null'
- 'SampleIsList for json correctly handled'

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: claude