chore: clean up dead code and deps (#4373)

- use `dep = { workspace = true }` instead of `dep.workspace = true` and
reformatted some Cargo.toml files to be more consistent with the style
used throughout the repo
- move some more deps to workspace deps
- remove dead voyager plugin data.rs/callback.rs files and use `Never`
instead
- remove some unused deps from some crates with
[cargo-machete](https://github.com/bnjbvr/cargo-machete) and
[unused_crate_dependencies](https://doc.rust-lang.org/beta/nightly-rustc/rustc_lint_defs/builtin/static.UNUSED_CRATE_DEPENDENCIES.html)
- note that both are imperfect and have many false positives/negatives,
so i only ran it manually locally and did not make a CI check for this

leaner deps means we get faster build times and better caching in CI, as
packages depend on a smaller portion of the lockfile. more improvements
can be made here (aside from just removing deps), but this is a good
start.