Function read_node

Recursively decode the inode at `idx` into a node, descending into directories. `budget` caps the total node count so a cyclic image cannot spin the render.

(
    vm: &VirtualMachine,
    base: u64,
    idx: u64,
    name: String,
    depth: usize,
    fds: &std::collections::HashMap<u64, u32>,
    budget: &mut usize,
)