Implement filter-based deletion for WeaviateVectorStore by leveraging the
existing ID-based deletion mechanism.
Key changes:
- Add doDelete(Filter.Expression) implementation that delegates to the existing
ID-based deletion method
- Use similarity search with filter to find matching documents first
- Delete matched documents by their IDs
- Add integration tests for filter deletion scenarios:
* Deleting by simple equality filter
* Deleting by string-based filter expression
This maintains consistency with other vector store implementations while
working around Weaviate's limitations in direct filtered deletion.
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