feat: add zsh plugin

[qq88976321]

Thank you for maintaining this useful project. I created this PR to add a zsh plugin that may make it easier for zsh users to use this project.

The main ideas is to use the zsh autoload builtin to define the code and code-connect functions.

I see that you add a unified install script in #10. However, a common way to install a zsh plugin is to git clone and source it in the .zshrc manually, or use a framework like oh-my-zsh and update the plugin list. Framework can also use git pull to upgrade the project automatically. So currently I directly added bin/ to $PATH to make code_connect.py callable instead of telling user to use the script to install and upgrade manually.

Welcome your feedback and suggestions.