zsh: rename lib/fzf to lib/10-fzf

This is to run this before a potential 20-atuin if I decide to keep
that.

diff --git a/zsh/lib/fzf.zsh b/zsh/lib/10-fzf.zsh
similarity index 100%
rename from zsh/lib/fzf.zsh
rename to zsh/lib/10-fzf.zsh