* Centralize session files to goose::session module
* Write session metadata and messages in jsonl
* Refactor CLI build_session to use goose::session functions
* Track session's token usage by adding optional session_id in agent.reply(...)
* NOTE: Only sessions saved through the updates goose::session functions will show up in GUI
Co-authored-by: Bradley Axen <baxen@squareup.com>