fix(ci): wrap uv install in retry block

[ko3n1g]

Summary

• Wraps the uv installer curl command in a retry loop (3 attempts, 10 s sleep between attempts) in all three jobs in install-test.yml.

Motivation

The install occasionally fails due to transient network issues. Without a retry, the entire CI job fails hard on a flaky download.

Example

- name: Install uv
  run: |
    for i in 1 2 3; do
      curl -LsSf https://astral.sh/uv/install.sh | sh && break
      echo "uv install attempt $i failed, retrying..."
      sleep 10
    done
    echo "$HOME/.local/bin" >> $GITHUB_PATH