[ZigPlanner] Add support for shell and build

[savil]

Summary

Adds basic support for shell and build.

Build Size optimization:

• If I include the zig nix package in the runtimePackages, then the image size
  is really large (700MB)
• But I believe the zig executable is standalone Executable is very big in Linux ziglang/zig#3660 (comment)
• So, I get the zig-executable's name by:
  • parsing the build.zig file (so unfortunate) to find the addExecutable line
  • fallback: if I fail to find exactly one addExecutable, then I fallback to installing the zig nix package and invoking zig build run
• the image size is 22MB

How was it tested?

shell:
in the testcase folder:

> devbox shell

(devbox)> zig build run
# see output
info: All your codebase are belong to us.

Don't be alarmed! Just a printout.

build:

> devbox build
> docker run devbox
info: All your codebase are belong to us.

[savil]

Current dependencies on/for this PR:

• main
  • PR [ZigPlanner] Add support for shell and build #141 👈

This comment was auto-generated by Graphite.

[mohsenari]

Can we change this message. It's a bit grim 😄

[savil]

Its the default zig hello world - I think their sense of humour is very Adams Family-esque, which I love :)

But yeah, I'll edit it to be less alarming.

[LucilleH]

Can use plansdk.AllFiles() if you want