> I have a ZSH prompt that shows the Git status of the current directory. Entering in a directory that has a Git repo freezes the terminal for several seconds.

For this specific problem, use a prompt that asynchronously updates git status. https://github.com/sindresorhus/pure is an example, and it contains all the primitives you need to implement your own async prompt. Otherwise good luck working on a huge repo like chromium, even on a faster machine.