Provide batch position and size information inside entity operations

This is a follow-up to: Azure/azure-functions-durable-extension#1511, Azure/azure-functions-durable-extension#1456

Now that the durable-extension exposes the batch position and batch size inside entity operations, we should expose them in the Python SDK as well.

Start by reviewing the Python SDK's entity operations and the two referenced durable-extension issues, #1511 and #1456, to understand the exposed batch position and size information. Done means making both values available inside Python entity operations and confirming the public SDK behavior.

Written by the indexing model from the issue text.