message: only compile the InMemoryApiClient for tests
diff: //! This module provides clients for the Xaynet coordinator API.
  mod http;
  -mod in_memory;
  +pub use self::http::{HttpApiClient, HttpApiClientError};
  -pub use self::{
  - http::{HttpApiClient, HttpApiClientError},
  - in_memory::{InMemoryApiClient, InMemoryApiClientError},
  -};
  +#[cfg(test)]
  +mod in_memory;
  +#[cfg(test)]
  +pub use self::in_memory::{InMemoryApiClient, InMemoryApiClientError};
  use crate::{
  mask::model::Model,
  