Cache ip address in network-public-ip plugin

[luftaquila]

Apply caching to the public IP just like the weather plugin, to prevent curl every few seconds.

[Theoreticallyhugo]

hi,
awesome work, thank you very much!
i have just one tiny request. on line 22 id prefer there to be no space between the icon and the ip, like so:
echo "$(get_tmux_option "@dracula-network-public-ip-label" "")$ip" > "${DATAFILE}"
i think that it's better to not have that extra padding unless a user wants to add it like so:
set -g @dracula-network-public-ip-label "icon-with-space "
however, im very open for debate on that one.
besides that im very happy to get this merged :D

[luftaquila]

Sure, I don't really care about that. I just updated the code as you suggested.

[Theoreticallyhugo]

thank you very much for your contribution!