building rust docs should not allow warnings

[jfly]

Right now, they build, but there is this warning:

$ cargo doc --workspace --open
...
warning: unresolved link to `Landings`
   --> crates/store/src/lib.rs:391:25
    |
391 |     /// Retrieves all [`Landings`]s.
    |                         ^^^^^^^^ no item named `Landings` in scope
    |
    = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
    = note: `#[warn(rustdoc::broken_intra_doc_links)]` on by default

[jfly]

This might be resolved by the pending work in the mob/nci branch.