feat: add new falkordb integration

[ghassenzaara]

Related Issues

• fixes Add New FalkorDB Integration #3007

Proposed Changes:

• Added FalkorDBDocumentStore to connect Haystack with FalkorDB graph databases.
• Added FalkorDBEmbeddingRetriever for standard vector searches.
• Added FalkorDBCypherRetriever for running custom GraphRAG Cypher queries.
• Ensured document metadata is flattened and stored directly on the graph nodes.
• Fixed vector insertion by casting arrays with vecf32() in Cypher queries.

How did you test it?

• Unit tests: Added basic component and serialization tests (hatch run test:unit).
• Integration tests: Verified writes, vector searches, and duplicate policies against a live database (hatch run test:integration).
• Linters: Passed all type-checking and formatting checks (hatch run test:types, hatch run fmt).

Notes for the reviewer

• Note the vecf32() explicit cast in the UNWIND cypher queries. This is specifically required by FalkorDB to parse vector embeddings correctly.

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.

[CLAassistant]

All committers have signed the CLA.