Enhance Neo4j service with error handling and testing improvements

[keremgocen]

Introduce error handling in the Neo4j service, implement a session interface for better testability, and add realistic test scenarios. Refactor code to improve clarity and maintainability.

• expands the interfaces we are using from Neo4j driver for testability, they are now moved into adapters.go to keep it tidy
• more unit test coverage in service.go now but ideally we'd like to introduce integration tests since not everything in the driver is exported so it's hard to test in unit tests (you need to do a lot of mocking and wrapping)

trello

[MacondoExpress]

Lovely ! 💯