feat: add support for named enum variant fields (#15)

tests/enum.rs

@@ -0,0 +1,20 @@
+use serde::Deserialize;
+use serde_inline_default::serde_inline_default;
+use serde_json::json;
+
+#[test]
+fn enum_default() {
+    #[serde_inline_default]
+    #[derive(Debug, PartialEq, Eq, Deserialize)]
+    #[serde(untagged)]
+    enum Test {
+        VariantWithFields {
+            #[serde_inline_default(255)]
+            test_int: u8,
+        },
+    }
+
+    let enum_test: Test = serde_json::from_value(json!({"VariantWithFields": {}})).unwrap();
+
+    assert_eq!(enum_test, Test::VariantWithFields { test_int: 255 })
+}