- Send notifications to ExtUI for M0/M1
- wait_for_user can be non-volatile (not changed by interrupt)
C / C++ compilers don't optimize away reads of non-volatile variables when a function call is used between accesses, because *any* variable could be changed by the function call. Since `wait_for_user` can't be changed without a function call, it should be non-volatile so the compiler can optimize away cases where it is read more than once without an intervening function call.
60e82e3929