feat(tvix/serde): add newtype & tuple deserialisation

Only missing enums at this point, but they're a bit of a beast.

Change-Id: I4ad47c034851f9a8794c81f39a5149a8ac1826e8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7716
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
Autosubmit: tazjin <tazjin@tvl.su>

tvix/serde/src/de_tests.rs

@@ -80,3 +80,18 @@ fn deserialize_struct() {
         }
     );
 }
+
+#[test]
+fn deserialize_newtype() {
+    #[derive(Debug, Deserialize, PartialEq)]
+    struct Number(usize);
+
+    let result: Number = from_str("42").expect("should deserialize");
+    assert_eq!(result, Number(42));
+}
+
+#[test]
+fn deserialize_tuple() {
+    let result: (String, usize) = from_str(r#" [ "foo" 42 ] "#).expect("should deserialize");
+    assert_eq!(result, ("foo".into(), 42));
+}