Background Tasks in radare2

Recently, I have been working on improving performance in Cutter, the radare2 GUI, especially when working with larger binaries. One major issue was that almost everything that accessed r2, such as updating the list of functions, strings, etc., was running on the main thread, and thus freezing the UI. While this is barely noticeable with smaller binaries, it can lead to a severe impact on usability for larger ones.