- improve script output - use sri hashes, same as recent versions of `nix`
- add flag to skip building updated providers - have the github action skip building providers so we don't need to handle build failures in the script - remove outdated `vendor` flag, all providers use `buildGoModule`
- use nix-prefetch for vendorSha256 - use no-out-link for nix-build - fix nixpkgs import path
- shellcheck / shfmt
