### What problem does this PR solve?

This PR addresses the inconsistency in property naming within the
codebase by renaming the 'chat' property to 'chat_id' in the session.py
file. This change aims to align the naming convention with other parts
of the application that refer to chat identifiers as 'chat_id', thereby
improving code clarity and maintainability.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)