[WIP][DartPlanner] shell and build support

[savil]

Summary

• devbox shell works
• devbox build experiences a TLS error. See below.

How was it tested?

Running into a TLS error when building using -v in dart pub get:

> BUILDKIT_PROGRESS=plain devbox build
27 3.091 IO  : Retry #2 for GET https://pub.dartlang.org/api/packages/test...

[savil]

Current dependencies on/for this PR:

• main
  • PR #150 👈

This comment was auto-generated by Graphite.

[savil]

hmm similar issue here: https://discourse.nixos.org/t/certificate-issues-in-pure-nix-shell-with-flutter-app/19814

[savil]

This gist is old, but suggests:

wrapProgram $out/bin/program \
  --set SSL_CERT_FILE "${cacert}/etc/ssl/certs/ca-bundle.crt"

[savil]

I had tried adding openssl and cacert in DevPackages but hadn't helped. I also tried various combinations of setting SSL_CERT_FILE env var.