Migrate async-rediscache to a vendored utility

[jb3]

🔧 Internalizing async-rediscache into pydis_core

Given that the upstream async-rediscache package has become largely unmaintained 🏚️ and no longer receives timely updates or fixes 🐛, it would be prudent to internalize its functionality within our own project.

By moving the relevant components into a vendored utility inside pydis_core 📦, we can ensure:

• Long-term stability 🛡️ - No more waiting on abandoned dependencies
• Maintained compatibility 🔗 - Better integration with the rest of our codebase
• Freedom to improve ✨ - Make necessary enhancements without depending on external maintenance

This approach also allows us to:

• Control versioning 🎯 - Manage releases on our own schedule
• Apply patches as needed 🩹 - Quick fixes without upstream delays
• Simplify dependency management 📊 - One less external dependency to worry about

Moving forward, this strategic decision will give us greater autonomy 🚀 and reduce technical debt associated with unmaintained dependencies! 💪