Performance improvement: cancel current and stacked searches

👋 When I run cs in a large file tree such that there is latency in the search, the search will start while I'm still typing. The current search keeps going but then the searches seem to stack, so that while I'm waiting for "full search query" it will spend time on the intermediate things I've typed, like "full s" and "full sear". It would be nice if the current search and any stacked searches were cancelled if there is a new search in the input buffer.

This is one of those things I did have in there at one point but kept running into deadlock issues. Its something I want to put back in. Once I get the new UI done I might revisit this properly.