Method occupy

vmm/src/app/id_pool.rs:39–45

(&mut self, id: T)

    }

    pub fn occupy(&mut self, id: T) -> anyhow::Result<()> {
        if self.allocated.insert(id) {
            Ok(())
        } else {
            bail!("id already occupied")
        }
    }

    pub fn allocate(&mut self) -> Option<T> {
        let mut id = self.start.clone();