add pump expander

rust/src/main.rs

@@ -2,6 +2,7 @@
 #![no_main]
 #![feature(never_type)]
 #![feature(string_from_utf8_lossy_owned)]
+#![feature(impl_trait_in_assoc_type)]
 #![deny(
     clippy::mem_forget,
     reason = "mem::forget is generally not safe to do with esp_hal types, especially those \