Add prompt caching toggle to main typing ui

I think it would be nice to have a quick access toggle like there is with thinking where you can enable caching in the chat. For most models it cost extra and only for 5 minutes. Being able to disable or set to extended easily would help alot save on cost to. Like most chats i will take over 5 minutes to respond so it would be better to disable it. But then in chats were im going back and forth alot its very useful.