Right now, Cursor (and friends) require that the generic type T be Sync + Send + Unpin + DeserializeOwned. This requirement was originally added because we used to buffer values of T in the Cursor, which needed them. Now that we buffer RawDocumentBuf and only deserialize at the end, we may be able to drop these requirements (besides DeserializeOwned).

Related: https://www.mongodb.com/community/forums/t/rust-driver-help-writing-a-generic-find-method/168846