ci: validate aarch64 in nix.yml and attach static binaries to releases
nix.yml: split the existing build job into lint (x86_64 only — fmt,
treefmt, deny, clippy, doc) and build (matrix over x86_64 and aarch64
— test, cmprss, cmprss-static, flake check). Architecture-independent
checks no longer run twice.
publish.yml: add a binaries job that builds cmprss-static via the flake
on x86_64 and aarch64 runners and attaches the resulting tarballs (with
SHA256 sidecars) to the GitHub Release. Runs only on release/dispatch
events — every-push validation is now covered by nix.yml.