nanocoap: State handler idempotentcy requirement
nanocoap: State handler idempotentcy requirement

Closes: https://github.com/RIOT-OS/RIOT/issues/12938

kYc0o/RIOT,OlegHahm/RIOT,miri64/RIOT,RIOT-OS/RIOT,basilfx/RIOT,smlng/RIOT,OTAkeys/RIOT,smlng/RIOT,RIOT-OS/RIOT,basilfx/RIOT,kaspar030/RIOT,ant9000/RIOT,yogo1212/RIOT,kYc0o/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,basilfx/RIOT,smlng/RIOT,kYc0o/RIOT,authmillenon/RIOT,ant9000/RIOT,OTAkeys/RIOT,ant9000/RIOT,OlegHahm/RIOT,kYc0o/RIOT,jasonatran/RIOT,jasonatran/RIOT,OTAkeys/RIOT,miri64/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,authmillenon/RIOT,ant9000/RIOT,yogo1212/RIOT,authmillenon/RIOT,OTAkeys/RIOT,basilfx/RIOT,authmillenon/RIOT,kaspar030/RIOT,yogo1212/RIOT,miri64/RIOT,RIOT-OS/RIOT,yogo1212/RIOT,ant9000/RIOT,kaspar030/RIOT,OlegHahm/RIOT,yogo1212/RIOT,kYc0o/RIOT,yogo1212/RIOT,jasonatran/RIOT,basilfx/RIOT,kaspar030/RIOT,jasonatran/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,miri64/RIOT,kaspar030/RIOT,authmillenon/RIOT,smlng/RIOT,jasonatran/RIOT,smlng/RIOT,miri64/RIOT