Reduce dependencies! 🗡️

I think we could massively reduce the number of dependencies, or at the very least the dependencies of our dependencies with feature flags.

Run `cargo tree` and take a peek.

Run `cargo tree` first to inventory the direct and transitive dependencies. Identify which dependencies can be removed or gated with feature flags; the work is complete only when the intended reduction and scope are made explicit.

Written by the indexing model from the issue text.