Prevent reeval if nothing changed

[maludwig]

I use the Random Prompt generator to have the same random prompt in all of my CLIPs, but there was a bug for the node, where it would always unconditionally recompute, which meant that when adding tiny things to a heavy compute graph, it took forever, rather than an eyeblink.

This change will only force recompute if the text, seed, or autorefresh properties change.

Since I don't truly understand the other nodes, this is just for the one I use.