fix(search): add #[derive(Deserialize)] to model types

[michaelhthomas]

It is recommended for data model types to implement serde's Deserialize trait. The majority of types in this library already implement Deserialize, but the search module is an exception, making it impossible to, for example, deserialize a search filter from JSON. This PR adds the #[derive(Deserialize)] macro to types which were previously missing it, making it possible to deserialize search filters, sorts, etc. using serde.