feat: Add TTL support for DynamoDB chat store

[arielbeckjit]

• Implement time-to-live (TTL) functionality for DynamoDB chat store
• Add optional ttl_seconds parameter to control item expiration
• Support custom TTL attribute name via ttl_attribute parameter
• Update message storage methods to include TTL when configured
• Add comprehensive test coverage for TTL feature

Description

Fixed depracation pydantic warning on _message_to_dict, and added new TTL functionality as for short term memory it might be nice to remove those items eventually.

Tested in real environment:

without configuring a ttl key name -

# Initialize DynamoDBChatStore
dynamo_chat_store = DynamoDBChatStore(
    table_name="TestShortTermMemory",
    ttl_seconds=60 * 60 * 24 * 30,  # 30 days
)

# Create a ChatSummaryMemoryBuffer with the DynamoDB chat store
chat_summary_memory = ChatSummaryMemoryBuffer.from_defaults(
    token_limit=50,
    chat_store=dynamo_chat_store,
    llm=llm,
    chat_store_key="slack_thread_id",  # Use session_id as the chat store key
)

with adding configured TTL name

# Initialize DynamoDBChatStore
dynamo_chat_store = DynamoDBChatStore(
    table_name="TestShortTermMemory",
    ttl_seconds=60 * 60 * 24 * 30,  # 30 days
    ttl_attribute="my_ttl",
)

# Create a ChatSummaryMemoryBuffer with the DynamoDB chat store
chat_summary_memory = ChatSummaryMemoryBuffer.from_defaults(
    token_limit=50,
    chat_store=dynamo_chat_store,
    llm=llm,
    chat_store_key="slack_thread_id2",  # Use session_id as the chat store key
)

Fixes # (issue)

_message_to_dict - fix deprecation.

New Package?

Did I fill in the tool.llamahub section in the pyproject.toml and provide a detailed README.md for my new integration or package?

• Yes
• [ X ] No

Version Bump?

Did I bump the version in the pyproject.toml file of the package I am updating? (Except for the llama-index-core package)

• [X ] Yes
• No

Type of Change

Please delete options that are not relevant.

• [ X ] Bug fix (non-breaking change which fixes an issue)
• [X ] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Your pull-request will likely not be merged unless it is covered by some form of impactful unit testing.

• [ Z ] I added new unit tests to cover this change
• I believe this change is already covered by existing unit tests

Suggested Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added Google Colab support for the newly added notebooks.
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I ran make format; make lint to appease the lint gods