use OS package manager for `zsh-autosuggestions` and `zsh-syntax-highlighting`

Currently they are downloaded with curl here:

https://github.com/bartekpacia/dotfiles/blob/1012461af091def57a53344b2e25cfc13ab39039/script/setup#L20-L40

| Package | Pacman Link | Homebrew Link |
|---------------------------------------------------------------------------------|--------------------------------------------------------------------------------|----------------------------------------------------------------------|
| [zsh-autosuggestions](https://github.com/zsh-users/zsh-autosuggestions) | [Pacman](https://archlinux.org/packages/extra/any/zsh-autosuggestions) | [Homebrew](https://formulae.brew.sh/formula/zsh-autosuggestions) |
| [zsh-syntax-highlighting](https://github.com/zsh-users/zsh-syntax-highlighting) | [Pacman](https://archlinux.org/packages/extra/any/zsh-syntax-highlighting) | [Homebrew](https://formulae.brew.sh/formula/zsh-syntax-highlighting) |
| [zsh-completions](https://github.com/zsh-users/zsh-completions) | [Pacman](https://archlinux.org/packages/extra/any/zsh-completions) | [Homebrew](https://formulae.brew.sh/formula/zsh-completions) |

There's also [zsh-autocomplete](https://github.com/marlonrichert/zsh-autocomplete) but I don't use it.

Start with the setup script at the linked lines 20-40 and inspect how the two Zsh packages are currently downloaded with curl. Compare the listed Pacman and Homebrew package links and determine the supported installation paths. Done means zsh-autosuggestions and zsh-syntax-highlighting are installed through the appropriate OS package manager rather than downloaded directly.

Written by the indexing model from the issue text.