fix(installer): fall back to official PyPI when mirror lags

[qin-ctx]

Description

Add a safe fallback for ov-install package installation when the default mirrors.volces.com index is behind official PyPI.

Related Issue

Fixes #1129

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• add a helper that retries pip install against official PyPI when the default mirror appears stale or temporarily unavailable
• keep honoring an explicit PIP_INDEX_URL override so user-selected indexes are not changed implicitly
• apply the same fallback logic to the normal, venv, and --break-system-packages install paths used by ov-install

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Manual verification:

• node --check examples/openclaw-plugin/setup-helper/install.js

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

N/A

Additional Notes

The immediate user workaround remains:
PIP_INDEX_URL=https://pypi.org/simple/ ov-install -y

[github-actions]

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