feat: make use of Nix files to set up dev env

[aduh95]

I first attempted to create the Docker image using Nix tools, but that ended up being too complicated, in the end it was easier to install Nix from the Dockerfile, and update the existing scripts to use Nix provided tools.

Worth noting the image contains a node built with all shared libs, similar to what builds test-shared GHA workflow on nodejs/node; we could certainly disable that to use the vendored static deps instead, the tradeoff being the build would take longer.

Fixes: #18

[joyeecheung]

Kicked off a build to see if the image built from this branch works https://github.com/joyeecheung/devcontainer/actions/runs/20376852332 (when it's done it'll be published to https://hub.docker.com/r/joyeecheung/node-devcontainer)

[joyeecheung]

LGTM with a suggestion on docs

[joyeecheung]

New test run: https://github.com/joyeecheung/devcontainer/actions/runs/20969928645

[aduh95]

New test run: https://github.com/joyeecheung/devcontainer/actions/runs/20969928645

Looks like it built successfully, not sure how to test it further though

[joyeecheung]

I gave it a try and I think this now needs an update in the devcontainer.json - at least, when paired with the default published image invariant (which uses static-lib). This is because devcontainers work by mounting the working dir, which overrides the .envrc copied within the container.

  "postStartCommand": "cp /home/developer/envrc/static-libs.envrc /home/developer/nodejs/node/.envrc && direnv allow /home/developer/nodejs/node"

If we add more published variant in the future, we can just add another devcontainer.json variant in the upstream that copy the corresponding envrc for a different paired image (e.g. "nodejs/devcontainer:shared-nightly" pairs with shared-libs.envrc, and then you can spin a devcontainer with a readily built shared lib configuration to test things)

[joyeecheung]

Opened nodejs/node#61414