What this PR does / why we need it:

This PR enhances the Qdrant online store implementation with improved type safety and error handling in the retrieve_online_documents_v2 method. The changes include:

1. Added proper type annotations and casting for entity keys and feature values
2. Improved error handling for timestamp parsing and value decoding
3. Enhanced null checks and type validation throughout the method
4. Added support for text-based search with fallback mechanisms

These changes make the Qdrant online store more robust and type-safe, while maintaining backward compatibility with existing functionality.

Which issue(s) this PR fixes:

Fixes #5115

Misc

Key improvements in this PR:

• Added explicit type casting using cast() from typing module
• Improved error handling for base64 decoding and timestamp parsing

The changes have been tested with both unit tests and integration tests to ensure backward compatibility and proper functionality.

@feast-dev/online-store-maintainers