[Feature Request]: Add a switchable zshrc injection function

[crazywhalecc]

Feature Description

Sometimes I need to use the system's PHP for debugging, and I need to temporarily cancel the PATH injected by Herd.

I noticed that the injection behavior of Herd seems to always be appending. When I modified the content injected last time, the content injected next time will be appended to the back without replacement. Maybe we can add an injected boundary comment like: # Herd inject start and # Herd inject end.

Is this feature valuable for other users as well and why?

In this way, you can control the current system PHP from the Herd interface, not just the PHP installed by Herd.