added nix package manager support

[reshmifrog]

• All tests passed. If this feature is not already covered by the tests, I added new tests.
• All static analysis checks passed.
• This pull request is on the dev branch.
• I used gofmt for formatting the code before submitting the pull request.
• Appropriate label is added to the PR for auto generate release notes.

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Added the support for nix package manager

[Balasubramanyamkosuri]

Review summary

Thanks for the Nix flexpack work — the flexpack/nix/ package and unit tests look solid.

Blocker: mergeArtifacts regression

This PR removes logic in entities/buildinfo.go that prefers a non-. artifact path when SHA1 matches:

if existingArtifact.Path == "." && newArtifact.Path != "." {
    (*intoArtifacts)[i] = newArtifact
}

That path preference is required for native UV/Poetry publish flows: artifacts are first recorded locally (path="."), then merged again after Artifactory upload with the real repo path. Without it, publish build-info can keep stale local paths and break property stamping / artifact browser links.

Please revert that hunk or add regression tests (UV publish ITs in jfrog-cli cover this).

Questions

1. bi nix uses hard-coded CollectBuildInfo("nix-build", "1") — is that intentional for a follow-up?
2. Confirm PR targets the correct base branch per repo policy.

Full structured review: see team doc docs/reviews/nix-pr-review.md in the Nix workspace.