demo_sessions should include size in bytes of the demo

[jayceslesar]

This allows us to display the size in the list_demos endpoint as well as change the demodata endpoint to include the size of the demo to get a progress bar

@get("/demodata", guards=[valid_key_guard, session_closed_guard, analyst_guard], sync_to_thread=False)
def demodata(request: Request, api_key: str, session_id: str) -> Stream:
    """Return the demo."""
    engine = request.app.state.engine
    bytestream_generator = demodata_helper(engine, api_key, session_id)
    file_size = os.path.getsize(session_id + ".dem") # Calculate the size of the file
    headers = {
        "Content-Disposition": f'attachment; filename="{session_id}.dem"',
        "Content-Length": str(file_size) # Include Content-Length header
    }
    return Stream(bytestream_generator, media_type=MediaType.TEXT, headers=headers)

To totally solve this issue:

• [x] change the 58fb39990d30_initialize.py file to include demo_length as an integer
• [x] get the size of the demo on the _close_session_with_demo function using os.stat
• [x] change the insert statement in that function to insert the integer returned in os.stat
• [x] add this number to the headers as seen in the above example when pulling that demo