Add escript CLI mode

[adamcstephens]

This allows deps_nix to be run as a standalone program rather than embedded inside a mix application. One significant benefit is that running as an escript bypasses the need to compile any deps completely. Since it's a regular nix package, one could add to their devshell or run one-off with nix run if using flakes.

𑁱 nix build .#

deps_nix on HEAD (9bfc3cc) [!]
𑁱 rm -rf _build deps.nix

deps_nix on HEAD (9bfc3cc) [!]
𑁱 time ./result/bin/deps_nix --no-app-config

________________________________________________________
Executed in  397.65 millis    fish           external
   usr time    1.83 secs      0.22 millis    1.83 secs
   sys time    0.68 secs      1.05 millis    0.68 secs

deps_nix on HEAD (9bfc3cc) [!]
𑁱 eza -l deps.nix
.rw-r--r-- 6.5k adam 11 Aug 22:30 deps.nix

deps_nix on HEAD (9bfc3cc) [!]
𑁱 eza -l _build
"_build": No such file or directory (os error 2)

This obviously implies the repo will need to keep its own deps.nix up to date. :)

[camelpunch]

Good idea! Very cool. I'll wait for the current build and take it for a spin. deps.nix staleness noted - I'll bake a check into CI, the release script or something.