** Marks a type to be mapped as a top level document in a MongoDB collection.
@FacetMeta { inherited = true }
facet class Entity {
    ** Name of the MongoDB collection that documents are stored under. 
    ** Defaults to the type name.
    const Str? name

    // we *could* add a 'pickleMode' arg here, but I don't know how useful it'd be
    // also - what if we ditch this @Entity facet and just use @MongoProp?