[Web Alpha] Improvements 1

[stevensJourney]

This adds some improvements after the initial alpha release.

• This updates the alpha-releases branch with the latest changes from master
• PowerSyncDatabase initialisation has been updated in README and example apps with better web compatibility. This removes any direct usage of dart:io and replaces some usages with universal_io.
• Package README is updated to point to Github releases for powersync_db.worker.js file. Now also includes more user-friendly instructions.
• The SQLite3 WASM init script has been migrated to a Dart script for better dev setup compatibility.
• Optimised powersync_db.worker.js compiled file size from 2Mb to 430kB.
• Updated Pana package analysing to only analyse published packages
• Added CI action for creating draft releases