Fixed adding float values into DynamoDB (#26562)

Thank you for contributing to LangChain!

- [x] **PR title**: Add float Message into Dynamo DB
  -  community
  - Example: "community: Chat Message History 


- [x] **PR message**: 
- **Description:** pushing float values into dynamo db creates error ,
solved that by converting to str type
    - **Issue:** Float values are not getting pushed
    - **Twitter handle:** VpkPrasanna
    
    
Have added an utility function for str conversion , let me know where to
place it happy to do an commit.
    
    This PR is from an discussion of #26543
    
    @hwchase17 @baskaryan @efriis

---------

Co-authored-by: Chester Curme <chester.curme@gmail.com>

libs/community/langchain_community/chat_message_histories/dynamodb.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import logging
+from decimal import Decimal
 from typing import TYPE_CHECKING, Dict, List, Optional
 
 from langchain_core.chat_history import BaseChatMessageHistory
@@ -17,6 +18,16 @@ if TYPE_CHECKING:
 logger = logging.getLogger(__name__)
 
 
+def convert_messages(item: List) -> List:
+    if isinstance(item, list):
+        return [convert_messages(i) for i in item]
+    elif isinstance(item, dict):
+        return {k: convert_messages(v) for k, v in item.items()}
+    elif isinstance(item, float):
+        return Decimal(str(item))
+    return item
+
+
 class DynamoDBChatMessageHistory(BaseChatMessageHistory):
     """Chat message history that stores history in AWS DynamoDB.
 
@@ -47,6 +58,8 @@ class DynamoDBChatMessageHistory(BaseChatMessageHistory):
             limit. If not None then only the latest `history_size` messages are stored.
         history_messages_key: Key for the chat history where the messages
             are stored and updated
+        coerce_float_to_decimal: If True, all float values in the messages will be
+            converted to Decimal.
     """
 
     def __init__(
@@ -62,6 +75,8 @@ class DynamoDBChatMessageHistory(BaseChatMessageHistory):
         ttl_key_name: str = "expireAt",
         history_size: Optional[int] = None,
         history_messages_key: Optional[str] = "History",
+        *,
+        coerce_float_to_decimal: bool = False,
     ):
         if boto3_session:
             client = boto3_session.resource("dynamodb", endpoint_url=endpoint_url)
@@ -83,6 +98,7 @@ class DynamoDBChatMessageHistory(BaseChatMessageHistory):
         self.ttl_key_name = ttl_key_name
         self.history_size = history_size
         self.history_messages_key = history_messages_key
+        self.coerce_float_to_decimal = coerce_float_to_decimal
 
         if kms_key_id:
             try:
@@ -159,6 +175,9 @@ class DynamoDBChatMessageHistory(BaseChatMessageHistory):
         _message = message_to_dict(message)
         messages.append(_message)
 
+        if self.coerce_float_to_decimal:
+            messages = convert_messages(messages)
+
         if self.history_size:
             messages = messages[-self.history_size :]