included command in `.zshrc` that eliminates duplicates in `$path`

[SebiBasti]

This is related to https://github.com/lewagon/dotfiles/issues/140

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Over time the $PATH variable can get quite bloated and have many duplicates inside.

typeset -U path

This takes care of this and checks $path to only include unique values e.g. it deletes all duplicates.

https://zsh.sourceforge.io/Guide/zshguide02.html#l24