[BUG] Neo4j crashing with nested attribute arrays

[Ataxia123]

Neo4j was crashing when entity/edge attributes contained nested structures (Maps of Lists, Lists of Maps) because attributes were being spread as individual properties instead of serialized to JSON strings.

Changes:

Serialize attributes to JSON for Neo4j (like Kuzu already does)
Update read path to handle both JSON strings and legacy dict format
Add integration tests for nested attribute structures
Maintain backward compatibility with existing code

PR: #1109