Expand description
Heap-backed containers for generated mode = "heap" message fields
(RFC-0033). Gated on alloc, which std implies — so a hosted consumer
gets these by asking for std and never has to name alloc. nros-serdes
gates its matching Serialize/Deserialize impls on the SAME feature and
receives it through the same forward, which is what issue 0598 was about.
Generated code refers to nros_core::heap::{Vec, String} so the same path
works in both crate and inline (build.rs) codegen modes.