#[module]Expand description
Marks a struct as an RHDL module shell for Story 1.1.
Generates Elaboratable that records directed ports via the builder session.
Fields marked #[functional_state] / #[rhdl::functional_state] (FR102) are
host-only soft state: kept on the Rust struct, skipped for port registration,
and never enter FrozenHir / freeze (AD-5 / AD-18).