[offline] Allow devbox to work offline if DNS fails

[mikeland73]

Summary

Fixes https://github.com/jetify-com/devbox/issues/1977

(with another hack).

Unfortunately the way we structure our flake makes it really difficult to remove our network requests (when state is stale). Ideally, the flake can be built off of local only nix store references, but that's a much bigger project.

In the meantime, this is a quick hack that fixes issue above.

How was it tested?

Added synthetic error that returns connection refused in the message. Ensures I was still able to run/shell with a stale state.

[sentry-io[bot]]

Suspect Issues

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

• ‼️ *exec.ExitError: nix print-dev-env --json "path:": <redacted exec.ExitError>* `go.jetpack.io/devbox/internal/nix in (Nix).Pri...` View Issue
• ‼️ Generic Error: error running script in Devbox: GET https://search.devbox.sh/v2/resolve?name=go... go.jetpack.io/devbox/internal/searcher in execG... View Issue
• ‼️ syscall.Errno: <redacted errors.withStack>: <redacted fs.PathError>: go.jetpack.io/devbox/internal/cuecfg in ParseFi... View Issue
• ‼️ *syscall.Errno: <redacted errors.withStack>: <redacted errors.withStack>: <redacted errors.withStack>: <redact...** go.jetpack.io/devbox/internal/shellgen in creat... View Issue

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