Update devcontainer and workflow dependencies

[PabloZaiden]

Summary

• Update Docker-in-Docker features from :3 to :4 and Node from :1 to :2 across examples and built-in templates.
• Update actions/checkout from @v4 to @v7.
• Update generated-config expectations for the new feature channels.

Other infrastructure references were already on their latest stable channels, and package dependencies required no version changes.

Validation

• bun test (154 passed, 4 live tests skipped)
• bun run test:fast
• bun run typecheck
• bun run build
• JSONC parsing for all devcontainer definitions

Live devcontainer tests were attempted with Docker and Dev Containers CLI 0.88.0 but were blocked by root-owned bind-mount permissions in this environment.

[Copilot]

Pull request overview

Updates devcontainer feature channels and workflow dependencies to newer major versions, and aligns tests/fixtures with the updated generated devcontainer configuration expectations.

Changes:

• Bump docker-in-docker feature from :3 → :4 across templates, examples, and related tests.
• Bump node feature from :1 → :2 for the TypeScript template and related tests.
• Update GitHub Actions workflow to use actions/checkout@v7.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/templates.ts	Updates built-in template feature references to docker-in-docker:4 and node:2.
tests/templates.test.ts	Updates template expectations (feature refs and pinned reference string) to match new feature channels.
tests/examples.test.ts	Updates generated-config assertions for examples to expect docker-in-docker:4 and node:2.
tests/core.test.ts	Updates resolve-workspace config expectation to docker-in-docker:4.
examples/smoke-workspace/.devcontainer/devcontainer.json	Updates example devcontainer to docker-in-docker:4.
examples/complex-workspace/.devcontainer/devcontainer.json	Updates example devcontainer to docker-in-docker:4 and node:2.
.devcontainer/devcontainer.json	Updates repository devcontainer to docker-in-docker:4.
.github/workflows/pr-tests.yml	Updates checkout action to actions/checkout@v7.

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