feat: create util module with shared mk_static macro

rust/src/main.rs

@@ -71,6 +71,7 @@ mod mqtt;
 mod network;
 mod plant_state;
 mod tank;
+mod util;
 mod webserver;
 
 extern crate alloc;

rust/src/util.rs

@@ -0,0 +1,10 @@
+macro_rules! mk_static {
+    ($t:ty,$val:expr) => {{
+        static STATIC_CELL: static_cell::StaticCell<$t> = static_cell::StaticCell::new();
+        #[deny(unused_attributes)]
+        let x = STATIC_CELL.uninit().write(($val));
+        x
+    }};
+}
+
+pub(crate) use mk_static;