refactor: create util module with shared mk_static

- use crate::util::mk_static in network module
- use crate::util::mk_static in mqtt module
- use crate::util::mk_static in hal module
- remove dead mk_static macro from esp module

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;