fix: address PR review feedback

- Remove deprecated custom_update_memory_prompt from MemoryConfig entirely
- Add MAX_BATCH=100 chunking guard to embed_batch in openai.py and azure_openai.py
- Move all inline imports (mem0.utils.*) to top-level in main.py
- Remove custom_update_memory_prompt from test fixture

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_main.py

@@ -61,7 +61,6 @@ def memory_custom_instance():
         config = MemoryConfig(
             version="v1.1",
             custom_instructions="custom prompt extracting memory in json format",
-            custom_update_memory_prompt="custom prompt determining memory update",
         )
         config.graph_store.config = {"some_config": "value"}
         return Memory(config)