cargo_metadata & krate coupling

[pinkforest]

Need to de-couple these and ensure they do not break between bumps...

https://dev.azure.com/cargo-geiger/cargo-geiger/_build/results?buildId=819&view=logs&j=022b0a5d-2698-5f72-7610-a845972a8b4c&t=33e4d865-0676-5964-ba63-59b88208e67d&l=350

error[E0609]: no field `krate` on type `&krates::Node<cargo_metadata::Package>`
   --> cargo-geiger\src\graph.rs:119:39
    |
119 |             let package = krates_node.krate.clone();
    |                                       ^^^^^

This is blocking https://github.com/rust-secure-code/cargo-geiger/pull/397