Add release download stats workflow

[eonist]

This PR adds a GitHub Actions workflow that tracks and reports release asset download counts.

What it does

• Runs daily at 02:00 UTC (configurable via cron schedule)
• Can also be triggered manually via workflow_dispatch
• Uses GitHub CLI (gh api) to query release asset download counts
• Displays total downloads across all releases
• Shows per-release breakdown in the workflow summary

Implementation

The workflow leverages the download_count field exposed by GitHub's REST API for release assets. GitHub CLI is pre-installed on ubuntu-latest runners, so no additional setup is needed.

Benefits

• Track adoption across different platforms (Linux x64/arm64, macOS, Windows)
• Measure interest in specific releases
• Historical data preservation (run daily to build time series)
• Zero cost (uses built-in GitHub features)

Related to the discussion about measuring GitHub release downloads and understanding which platforms users prefer.