Box to save memory

A Rust developer reduced memory usage from 895 MB to 420 MB by boxing optional structs during JSON deserialization. The key insight is that `Option<BigStruct>` in Rust still occupies the full size of `BigStruct` even when `None`, unlike reference-based languages like Java or Python. The fix involves changing `Option<SmithyReference>` fields to `Option<Box<SmithyReference>>` and implementing a custom Serde deserializer that discards empty structs instead of storing them. Memory measurement was done using jemalloc via a Cargo feature flag. The post also notes that while boxing increases heap fragmentation and adds CPU overhead for deserialization, the overall performance improved due to reduced memory pressure.