Accept xz prebuilt archives

[macayu17]

Prerequisite

• Please consider implementing the feature as a hook script or plugin as a first step.
  • This updates the existing prebuilt-download updater.
• My PR addresses the following pyenv issue (if any)
  • Part of Provide prebuilt CPython for common environments pyenv#2334. It does not close the issue.

Description

• Here are some details about my PR
  • Allows pythons/update.sh to accept .tar.xz prebuilt archives while retaining .tar.gz support.
  • Updates the existing updater test to use the .tar.xz format produced by pyenv-binary.
  • Fixes the Update downloads failure in the binary publishing workflow.

Tests

• My PR adds the following unit tests (if any)
  • The updater test passes in a Linux container.
  • Both .tar.xz indexing and existing .tar.gz compatibility were checked.
  • ShellCheck and git diff --check pass.

---

Summary by cubic

Drops the .tar.gz-only filename check in pythons/update.sh, so the updater now accepts .tar.xz prebuilt archives (and any safe archive name from metadata) while retaining .tar.gz support, fixing the binary publishing workflow's Update downloads failure. Rewrites the updater test in Bats to cover both archive formats, idempotent re-runs, failed runs leaving files unchanged, unsafe-name rejection, and missing-file failures, and documents the Bats test command in README.md.

^{Written for commit d74d187. Summary will update on new commits.}

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[cubic-dev-ai]

All reported issues were addressed across 2 files

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[macayu17]

@native-api Could you take a look when you have a chance?

[native-api]

Maybe use bats?
There are only a few tests, but you already have plenty of test framework code.

[macayu17]

Switched the updater tests to Bats, removed the leftover default and redundant metadata validation, and kept the unsafe-name and missing-artifact checks.

[cubic-dev-ai]

All reported issues were addressed across 3 files (changes from recent commits).

<sub>Tip: Review your code locally with the cubic CLI to iterate faster.

Re-trigger cubic</sub>

[cubic-dev-ai]

All reported issues were addressed across 2 files (changes from recent commits).

<sub>Tip: Review your code locally with the cubic CLI to iterate faster.

Re-trigger cubic</sub>