feat(graph_builder): add retry mechanism for Zep Cloud connection failures

[EuanTop]

Description

Adds automatic retry mechanism to handle transient network errors when connecting to Zep Cloud API. This prevents graph build failures caused by temporary connection issues such as "Connection reset by peer" (errno 54).

The retry logic uses exponential backoff (2s, 4s, 6s) and provides detailed progress feedback to users.

Changes

• Added retry logic (max 3 attempts) to create_graph() method in graph_builder.py
• Added retry logic to set_ontology() method for robust ontology configuration
• Added retry logic to add_text_batches() method for batch data uploads
• Implemented exponential backoff strategy with detailed console logging
• Added progress messages showing retry attempts and wait times

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation

Testing

• Manually tested with unstable network conditions
• Verified retry mechanism triggers on connection failures
• Confirmed successful graph creation after transient network errors
• Tested with various network interruption scenarios

Related Issue

Related to #60 - Improves robustness when connecting to Zep Cloud API

Additional Notes

This change is backward compatible and doesn't modify the API interface. The retry mechanism is transparent to users and only activates when network errors occur.