[devbox global] add `--omit-nix-env` flag for shellenv/shell/run commands

[savil]

…vars

Summary

In this PR, we change devbox global shell environment to omit the env-vars from nix print-dev-env. Instead, we rely on the nix profile that Devbox manages to introduce the global packages into PATH. As before, nix profile continues to be generated from the buildInputs from nix print-dev-env <devbox-generated-flake>.

The motivation is:

1. devbox global adds a bunch of nix stdenv packages to the top of your $PATH variable, which can cause conflicts when trying to compile or build projects on your machine.
2. devbox global also sets a global PYTHONPATH variable that interferes with other packages, as well as python scripts that are installed/running on the host. This global PYTHONPATH is unnecessary because any python binaries installed by the user are already wrapped with the PYTHONPATH

Implementation notes:

• Sets Devbox.envForPackageBins boolean setting that controls whether the Devbox Environment is optimized for executing package binaries, or for developing software using the packages.
  • [x] see if this can be passed down as a function parameter (see #2159)
• Adds flagDefaultOptions to shellEnvCmd. This is a nicer way of overriding the defaults in global, even for the --recompute flag that we had done before.
• Refactors code into a devbox.execPrintDevEnv function to remove some of the complexity from the devbox.computeEnv function (thanks to finger-wagging by our linter tool ;) ).

TODO:

• [x] Verify omitNixEnv is still properly handling the useNixPrintDevEnvCache call paths

How was it tested?

CICD tests should pass

TODO:

• [x] Ensure the python global scenario works
• [x] Ensure we can use common packages (fzf, ripgrep, etc.) in devbox global
• [x] Thanks to @gcurtis vetted this PR helps resolve issues with a couple of repos: (rust: https://github.com/zed-industries/zed.git) and (golang with cgo: github.com/Code-Hex/vz/example/macOS)

[sentry-io[bot]]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ *Generic Error: <redacted errors.fundamental>* `go.jetpack.io/devbox/internal/devpkg in (Packa...` View Issue
• ‼️ *exec.ExitError: <redacted errors.withStack>: <redacted errors.withStack>: <redacted exec.ExitError>** go.jetpack.io/devbox/internal/shellgen in makeF... View Issue
• ‼️ Generic Error: GET https://search.devbox.sh/v2/resolve?name=dnsutils&version=latest: unexpected status code 429 ... go.jetpack.io/devbox/internal/searcher in execG... View Issue
• ‼️ Generic Error: GET https://search.devbox.sh/v2/resolve?name=python&version=latest: unexpected status code 429 To... go.jetpack.io/devbox/internal/searcher in execG... View Issue
• ‼️ *json.SyntaxError: <redacted errors.withStack>: <redacted errors.withStack>: <redacted errors.withStack>: <redact...* `go.jetpack.io/pkg/filecache in (Cache[...]).Get` View Issue

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