Merge named and shorthand class attributes

[eboody]

Summary

• normalize named class attributes into the same rendering path as class shorthand so mixed forms emit one class attribute
• preserve ordering across shorthand, literal, dynamic, and optional class fragments instead of emitting duplicate class attributes
• add regression coverage for mixed shorthand with literal, dynamic, and optional named class values

Closes #496.

Testing

• cargo test mixed_shorthand_and_
• cargo test --test basic_syntax