feat(core): derive `Debug` for `BlockQueries`

feat(core): derive `Debug` for `BlockQueries`

`BlockQueries` is half of `CanonicalTask::Output`, so without `Debug` the
task's own output tuple isn't `Debug` — `dbg!(chain.run_task(task))` and
`.unwrap()` on a `Result` in that position don't compile. Its neighbours
`BlockCandidateResolution` and `Canonical` already derive it (Rust API
guideline C-DEBUG).

Covered by formatting the output tuple in the existing `CanonicalTask`
test, so the derive can't be dropped without a test failing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NND8BhEmYTYdLRv4dbUUro