Apologies, I missed your post.
Wiring.h is one of the low level includes deep in the arduino core.
Not sure if you followed my other posts but there is a bug with the MKRWAN1300 that will not let let achieve less than about 1.16mA sleep current. You can hack the board to fix it but it is a pretty complicated hack. Arduino said they are working on a board rev but I do not know when this will be available.