feat: ArcadeDB graph database adapter

[lvca]

Summary

• Adds a new graph adapter for ArcadeDB, the open-source multi-model database (Apache 2.0)
• ArcadeDB implements the Neo4j Bolt wire protocol natively, so this adapter uses the standard neo4j async Python driver — no custom driver needed
• All queries use standard OpenCypher (97.8% TCK compliance)
• Includes full GraphDBInterface implementation, example, test, and README with Docker quickstart

What's included

File	Description
cognee_community_graph_adapter_arcadedb/__init__.py	Package init with register() function
cognee_community_graph_adapter_arcadedb/arcadedb_adapter.py	Full GraphDBInterface implementation (~600 lines)
examples/example.py	Working example with ArcadeDB connection
tests/test_arcadedb.py	Edge persistence test (3 nodes, 3 relationship types)
pyproject.toml	Package metadata with cognee[neo4j]>=0.5.2 dependency
README.md	Installation, Docker quickstart, usage example

Testing

Tested locally against ArcadeDB v26.2.2 in Docker with Bolt protocol enabled:

docker run -d --name arcadedb -p 2480:2480 -p 7687:7687 \
  -e JAVA_OPTS="-Darcadedb.server.rootPassword=arcadedb -Darcadedb.server.defaultDatabases=cognee[root]{} -Darcadedb.server.plugins=Bolt:com.arcadedb.bolt.BoltProtocolPlugin" \
  arcadedata/arcadedb:latest

All tests pass: node creation, edge creation with multiple relationship types, query verification.

Context

This follows up on topoteretes/cognee#2239 where @Vasilije suggested the adapter should live in cognee-community.

[lvca]

@Vasilije1990 thanks for merging it! Do you need anything from me to appear in the adapters (README.md)?

[AKC777]

If ArcadeDB supports not only graphs, but also a vector database... Maybe it makes sense to connect vectors to ArcadeDB as well?

[lvca]

It makes sense. I see other implementations are hybrid: graph + vector.... working on it

[lvca]

@AKC777 Great suggestion! ArcadeDB does support vector search natively with HNSW indexes and the vectorNeighbors() function.

I've just opened PR #94 that upgrades the ArcadeDB adapter from graph-only to a hybrid adapter (like FalkorDB), implementing both GraphDBInterface and VectorDBInterface in a single class.

Graph operations continue to use Bolt/Cypher, while vector operations use ArcadeDB's HTTP API for SQL-based HNSW indexing and KNN search. This means Cognee users can use ArcadeDB as a unified graph+vector store without needing a separate vector database.

[lvca]

It's ready! #94