Install lsql offline in CI to avoid GitHub API rate-limit 403s

[FastLee]

Summary

The Install LSQL step in push.yml intermittently fails with:

Error: version: versions: refresh: github request failed: 403 Forbidden
  GET https://api.github.com/repos/databrickslabs/lsql/releases

databricks labs install fetches both the release list and the source zipball from api.github.com anonymously — the CLI's cmd/labs/github client uses http.DefaultClient with no Authorization header and reads no GITHUB_TOKEN/GH_TOKEN on any version (verified against v0.292.0 and main). So it hits GitHub's 60 req/hr unauthenticated rate limit, which is shared across GitHub Actions runner IPs.

PR #4857 added GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} to the step, but that variable is silently ignored by the CLI — it was a no-op, and the run only went green because it happened to land in a window with rate-limit budget.

Fix

Pre-fetch the release list and source archive with authenticated gh (5,000 req/hr), seed the CLI's local cache (~/.databricks/labs/lsql/cache) and lib dir (~/.databricks/labs/lsql/lib), then run databricks labs install lsql --offline so the CLI makes no GitHub API calls at all.

Test plan

• Verified locally end-to-end: seed cache + unpack lib + install --offline produces a working lsql plugin (databricks labs installed lists lsql v0.17.0) and databricks labs lsql fmt runs with no diff.
• CI build / fmt job passes the Install LSQL step.

This pull request and its description were written by Isaac.

[github-actions]

✅ 2/2 passed, 20s total

_{Running from acceptance #9036}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.79%. Comparing base (22ba51e) to head (ed30c40).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4865   +/-   ##
=======================================
  Coverage   87.79%   87.79%           
=======================================
  Files         123      123           
  Lines       17595    17595           
  Branches     3717     3717           
=======================================
  Hits        15448    15448           
  Misses       1458     1458           
  Partials      689      689           

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