Add initial project structure and implement async main for Pico W

tests/example_test.rs

@@ -0,0 +1,13 @@
+#![no_std]
+#![no_main]
+
+use defmt_rtt as _;
+use panic_probe as _;
+
+#[defmt_test::tests]
+mod tests {
+    #[test]
+    fn it_works() {
+        assert!(true);
+    }
+}