Macro budget 

macro_rules! budget {
    ( $( $field:ident : $value:expr ),* $(,)? ) => { ... };
}

Construct Some([``crate::Budget``]) from Default and a list of field assignments.

This macro returns Some(Budget) (instead of just Budget) so it can be embedded directly inside crate::options! as the value for Options::budget.

Example:

let options = serde_saphyr::options! {
    budget: serde_saphyr::budget! {
        max_nodes: 30,
    },
};