fix: graphiti search only connect with default db 'neo4j' and custom database config invalid

[Bit-urd]

Summary

Fixes Neo4j driver to properly handle custom database configurations. The driver now correctly passes the database parameter
instead of hardcoding the default 'neo4j' database name.

Type of Change

• Bug fix
• New feature
• Performance improvement
• Documentation/Tests

Objective

For new features and performance improvements: N/A - This is a bug fix.

Testing

• Unit tests added/updated
• Integration tests added/updated
• All existing tests pass

Breaking Changes

• This PR contains breaking changes

Checklist

• Code follows project style guidelines (make lint passes)
• Self-review completed
• Documentation updated where necessary
• No secrets or sensitive information committed

Related Issues

#851

[danielchalef]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[Bit-urd]

I have read the CLA Document and I hereby sign the CLA

[Bit-urd]

this is my test case

import asyncio
from datetime import datetime
from os import getenv

from graphiti_core.driver.neo4j_driver import Neo4jDriver
from graphiti_core.graphiti import Graphiti
from graphiti_core.utils.maintenance import clear_data


async def main():
    password = getenv("NEO4J_PASSWORD")
    # Default database test
    print("=== Default database (neo4j) ===")
    driver1 = Neo4jDriver("bolt://10.0.0.2:7687", "neo4j", password, "neo4j")
    client1 = Graphiti(graph_driver=driver1)
    await client1.build_indices_and_constraints()
    await clear_data(client1.driver)

    await client1.add_episode(
        "episode1",
        "User Tom purchased an iPhone",
        "Test episode data",
        datetime.now()
    )
    results1 = await client1.search("Tom")
    print(f"Default database search results: {results1} items")
    await driver1.close()
    
    # Custom database test
    print("\n=== Custom database (testdb) ===")
    try:
        driver2 = Neo4jDriver("bolt://10.0.0.2:7687", "neo4j", password, "biturd")
        client2 = Graphiti(graph_driver=driver2)
        await client2.build_indices_and_constraints()
        await clear_data(client2.driver)

        await client2.add_episode(
            "episode2",
            "User John purchased a Iphone",
            "Test episode data",
            datetime.now()
        )
        results2 = await client2.search("John")
        print(f"Custom database search results: {results2} items")
        await driver2.close()
    except Exception as e:
        if "DatabaseNotFound" in str(e):
            print("Successfully connected to testdb database (database doesn't exist, as expected)")
        else:
            print(f"Error: {e}")
    
    print("\nDatabase parameter fix test completed")

if __name__ == "__main__":
    asyncio.run(main())

before fix ：

after fix：

[bfhealy]

This would also address #798