Per conversation with Antonio, I've suggested enabling full LTO; right
now we use a crate-local ThinLTO, which does not inline function calls
across crates.

| Configuration    | Current main (788f97e) | Thin LTO  | Full LTO  |
|------------------|------------------------|-----------|-----------|
| Size in bytes    | 158806721              | 155868753 | 111115553 |
| % of `main` size | 100%                   | 98.14%    | 69.96%    |
| Size in bytes (no debug info) | 129186657 | 127942929 | 108281345 |