f03320c3

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Dedupe flake outputs and tune NixCI dependency discovery

- Expose each derivation under exactly one attribute (drop packages.bombadil
  alias and the checks.* that merely re-listed packages/devShells), so NixCI
  no longer schedules the same build under several names.
- Add nix-ci.nix enabling synchronous dependency discovery, so the shared
  dependency derivation is built once, up front, instead of every job
  recompiling dependencies in parallel. Defer the expensive cross/test builds
  behind clippy to fail fast.

Timeline