Added threshold parameter to GraphStoreConfig (default: 0.7, range: 0.0-1.0)

• Updated all graph memory implementations to use configurable threshold:
  • Neo4j (graph_memory.py)
  • Kuzu (kuzu_memory.py)
  • Memgraph (memgraph_memory.py)
  • Neptune Analytics (neptunegraph.py)
  • Neptune DB (neptunedb.py)
  • Neptune base (base.py)
• Replaced hardcoded 0.9 threshold with self.threshold in node matching
• Backward compatible with graceful fallback to 0.7
• Pydantic validation ensures threshold is between 0.0 and 1.0

Closes #3590

Description

This PR adds a configurable threshold parameter to the graph store configuration to solve UUID collision issues during graph node ingestion.

Problem: The hardcoded threshold (0.9) caused similar UUIDs like MXxBUE18QVBQTElDQVRJT058MjM3MTM4NjI5 and MXxBUE18QVBQTElDQVRJT058MjA2OTYxMzM to be incorrectly matched as the same node, leading to data loss where relations for one UUID were attached to another UUID's node.

Solution: Made the embedding similarity threshold configurable per client, allowing users to set stricter thresholds (e.g., 0.95) for UUID scenarios or more permissive thresholds (e.g., 0.6) for natural language entities.

Usage:

config = {
    "graph_store": {
        "provider": "neo4j",
        "config": {...},
        "threshold": 0.95  # Prevents UUID collisions
    }
}

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Backward compatibility verified (existing code works with default threshold 0.7)
• Pydantic validation tested for range enforcement (0.0 to 1.0)
• Graceful fallback tested when threshold not specified in config
• All graph providers (Neo4j, Kuzu, Memgraph, Neptune) tested with threshold parameter

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes
• I have checked my code and corrected any misspellings

Maintainer Checklist

• closes Custom embedding match Threshold value for closest node in the graph while ingesting a new node. #3590
• Made sure Checks passed