Add multi-field OR filter functionality

[doubledare704]

Pull Request Template for FastCRUD

Description

This PR implements the feature requested in issue #117, adding support for OR conditions across multiple fields in FastCRUD.

Changes

• Added a new _handle_multi_field_or_filter method to the FastCRUD class to handle OR conditions across multiple fields
• Updated the _parse_filters method to recognize a special _or parameter for multi-field OR filtering
• Added comprehensive tests for the new functionality
• Updated documentation in docs/advanced/filters.md to explain how to use the new feature

Tests

Describe the tests you added or modified to cover your changes, if applicable.

Checklist

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• I have added necessary documentation (if appropriate).
• I have added tests that cover my changes (if applicable).
• All new and existing tests passed.

Additional Notes

Include any additional information that you think is important for reviewers to know.

[igorbenav]

Looking great as always!
Thanks, @doubledare704