9df6f775

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

Add a Nix flake for fast, incrementally-cached CI

Builds bombadil with crane and the oxalica rust-overlay (x86_64-linux):
- default/static-musl/aarch64-musl CLI binaries, the wasm inspect UI,
  the npm package, plus clippy, rustfmt and the test suite as checks.
- A single shared dependency derivation whose source is reduced by crane to
  cargo metadata only, so editing source code never rebuilds dependencies.
  See nix/experiments/deps-cache-stability.sh for a runnable proof.
- wasm-bindgen-cli pinned to 0.2.125 to match the wasm-bindgen crate.

nix flake check builds everything; this is what NixCI runs.

Timeline