updated to 1.21.5 and 1.21.6
Untested on 1.21.9.1-21.10
Added support for 1.21.5
Support for 1.21.4
Support added for 1.21.2 and 1.21.3 but 1.21.3 has not been tested
Now supports JAVA_17 and version below 1.20.6
Flight Speed Changer intial release
Tested on 1.20.6 1.21 1.21.1