better parser errors

error_test/parser/attribute_errors.sui

@@ -0,0 +1,22 @@
+# Attribute errors
+
+# Missing attribute name
+@ 42
+
+# Invalid attribute argument
+@deprecated invalid
+
+# Missing equals in key-value attribute
+@version "1.0"
+
+# Missing closing parenthesis in attribute
+@deprecated("old", reason = "new"
+
+# Invalid attribute syntax (missing value after =)
+@version =
+
+# Attribute on invalid location
+fn test() -> int
+    @inline
+    let x = 5
+    x