Cache scanned folder files

Between calls to `/prompt` and when starting the program there is a lot of redundant work done in rescanning directories multiple times. This is the most significant slowdown I've encountered since I have thousands of models and each call to `object_info` can take up to half a minute per group of scans. And those scans are repeated many times since there is no caching, so that can make the call to `/object_info` time out