Improve zellij exit to reduce error

[xuanyuan300]

Currently, when zellij exits, a number of errors are printed in the logs, such as the following error.

rors.tuna.tsinghua.edu.cn-df7c3c540f42cdbd/zellij-utils-0.39.1/src/errors.rs:632]: Panic occured:
             thread: screen
             location: At /home/wjd/.cargo/registry/src/mirrors.tuna.tsinghua.edu.cn-df7c3c540f42cdbd/zellij-server-0.39.1/src/lib.rs:817:18
             message: Program terminates: a fatal error occured

Caused by:
    0: failed to remove client 1
    1: Failed to log and report session state
    2: failed to send message to background jobs
    3: Originating Thread(s)
       	1. stdin_handler_thread: AcceptInput
       	2. ipc_server: ClientExit
       	3. screen_thread: RemoveClient
       
    4: failed to send message to channel 

This may lead the user to believe that a panic has occurred, but it does not actually affect usage.
Since there are multiple loops in zellij (server, screen, pty, plugin) and they async communicate through channels, the order in which the loops are closed may affect the errors.
This PR optimizes the stop logic of zellij to minimize the occurrence of errors.