better parser errors

error_test/parser/struct_errors.sui

@@ -0,0 +1,30 @@
+# Struct syntax errors
+
+# Missing struct name
+struct
+    x: int
+    y: int
+end
+
+# Missing field type
+struct Point
+    x
+    y: int
+end
+
+# Missing colon in field
+struct Point
+    x int
+    y: int
+end
+
+# Missing end keyword
+struct Point
+    x: int
+    y: int
+
+# Invalid field separator (semicolon instead of comma)
+struct Point
+    x: int;
+    y: int
+end