Switch to custom fc repo; Improve build system

[ValentaTomas]

Note

Build pipeline now uses a custom Firecracker repo, parses versions into a matrix, builds in parallel, checks upstream CI, and conditionally uploads to GCS and creates per-version releases.

• CI/Workflows:
  • Add reusable github/workflows/build.yml to build a single version/hash/version_name and upload artifact.
  • Revamp fc-versions.yml:
    • Add concurrency control.
    • Prepare matrix from firecracker_versions.txt via script; build using reusable workflow.
    • Check upstream CI for each commit; gate publishing on success and main.
    • Collect artifacts, upload to GCS, and create tagged GitHub releases per version_name.
• Build:
  • build.sh now clones e2b-dev/firecracker, validates tag+hash, builds firecracker binary, and outputs to builds/<version_name>/.
• Scripts:
  • scripts/parse-versions-with-hash.sh resolves versions to full hashes and normalized version_name JSON.
  • scripts/check-fc-ci.sh inspects commit statuses/check-runs via GitHub API and reports pass/fail.
• Docs:
  • Update README.md to describe version parsing, matrix builds, CI gating, GCS upload, and releases; rename project to fc-versions.

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[ValentaTomas]

Not sure if FC tests should be run here or in the FC repo—in the FC repo, there might not be a way to enforce this as we will have multiple branches for versions, that won't be merged.

But somehow requiring that all checks for the specific hash passed might work.

EDIT: Adding CI status checks here and triggering tests on each push to the FC repo.

[tomassrnka]

@ValentaTomas yes, maybe we should run all FC checks with the build, i will revert the question - why not here? we want to have stable / tested version done, maybe we should actually add it here in next PR.

[ValentaTomas]

@jakubno lgty?