feat: add ui test

rtic/ui/custom_section.rs

@@ -0,0 +1,18 @@
+#![no_main]
+
+#[rtic::app(device = lm3s6965)]
+mod app {
+    #[shared]
+    struct Shared {
+        #[link_section = ".custom_section"]
+        foo: (),
+    }
+
+    #[local]
+    struct Local {}
+
+    #[init]
+    fn init(_cx: init::Context) -> (Shared, Local) {
+        (Shared { foo: () }, Local {})
+    }
+}