nix: add flake

[jdek]

Adds a Nix flake providing a package and dev shell for x86_64-linux, aarch64-linux and aarch64-darwin. The derivation lives in package.nix; default.nix and shell.nix are thin wrappers around it, so nix-build/nix-shell still work without flakes.

Fixes #34 correctly on macOS. The incompatible fasl-object version error is not a Chez packaging problem: Nix's fixupPhase strips $out/lib, and Apple's strip truncates the fasl object entirely. Corrected with stripDebugList = [ "bin" ].

test/data3.ss:395 glob-expands the source root, so its expectation now includes flake.nix and flake.lock.

Tested on aarch64-darwin and x86_64-linux.

user@machine:~$ echo '((lambda (n) (+ n n)) 4)' | nix run github:jdek/schemesh/flake
shell user@machine:~:((lambda (n) (+ n n)) 4)
8
shell user@machine:~:
user@machine:~$

[cosmos72]

Thanks for the contribution.

Unluckily this has the same problem as the older #13:
I don't know enough about Nix to validate the contributed code

[jdek]

I now additionally added a GitHub Actions workflow to automate exercising of the paths to validate functionality. Hope that helps.