Fix: Search results stop after first model due to incorrect indentation (#127)

[qzMalekuz]

Fixes an issue where search results were only returned for the first model due to incorrect indentation causing an early return inside the loop.

Changes:

• Corrected loop indentation in _xapian_search to ensure all models are processed
• Added unit test to verify results are returned across multiple models
• Mocked external dependencies (xapian, conf) for isolated testing

This resolves #127.