feat: warn on stale zst shards repodata

[mohamedawnallah]

Description

In this PR, we warn when stale repodata.json.zst or repodata_shards.msgpack.zst files exist, but their outputs are disabled, preventing clients from silently consuming outdated package metadata. It also adds integration tests to verify that it has the intended behavior changes and to ensure no regressions.

Closes #1856.

Rattler Index Demo Update

Before	After
before-stale-zst-shards-warning.mov	after-stale-zst-shards-warning.mov

How Has This Been Tested?

With integration tests in place in tests/integration/stale_output_tests.rs.

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.

Tools: {Claude Code}

I used Claude Code to learn and explore relevant parts of rattler codebase. I also used it to write boilerpalate rust test code

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added sufficient tests to cover my changes.

[mohamedawnallah]

Hi @baszalmstra, @wolfv I am new to the Rattler codebase, and I am genuinely interested in contributing. I have submitted that PR to resolve this existing issue #1856. I have looked at the GitHub CI tests seems they are related to the changeset introduced in this PR #2132.

Would love to receive any feedback. Thank you!