lance-db-name_exists-ag-2655 (#2024)

## Description

- Added `name_exists` function for LanceDb. 

Fixes #2017

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## Type of change

Please check the options that are relevant:

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] Model update (Addition or modification of models)
- [ ] Other (please describe):

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## Checklist

- [ ] Adherence to standards: Code complies with Agno’s style guidelines
and best practices.
- [ ] Formatting and validation: You have run `./scripts/format.sh` and
`./scripts/validate.sh` to ensure code is formatted and linted.
- [ ] Self-review completed: A thorough review has been performed by the
contributor(s).
- [ ] Documentation: Docstrings and comments have been added or updated
for any complex logic.
- [ ] Examples and guides: Relevant cookbook examples have been included
or updated (if applicable).
- [ ] Tested in a clean environment: Changes have been tested in a clean
environment to confirm expected behavior.
- [ ] Tests (optional): Tests have been added or updated to cover any
new or changed functionality.

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## Additional Notes

LanceDb natively does not allow `name_exists`. This is a very
inefficient workaround. To be updated when native search for a doc name
is added by LanceDb. `name_exists` is used by the `WebsiteKnowledgeBase`

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Co-authored-by: Dirk Brand <[email protected]>

libs/agno/agno/vectordb/lancedb/lance_db.py

@@ -326,4 +326,7 @@ def delete(self) -> bool:
         return False
 
     def name_exists(self, name: str) -> bool:
-        raise NotImplementedError
+        if self.table is None:
+            return False
+        result = self.table.search().select(["payload"]).to_pandas()
+        return any(row["payload"].get("name") == name for _, row in result.iterrows())