Mangle is now hosted on Codeberg

[burakemir]

The Mangle repo is now hosted on Codeberg:

• go implementation: https://codeberg.org/TauCeti/mangle-go
• rust implementation: https://codeberg.org/TauCeti/mangle-rs

This changes the Mangle development process:

• The go module is now codeberg.org/TauCeti/mangle-go - please update your go.mod
• Mangle v0.5 uses the new go module name.
• The Codeberg repos are the new source of truth. Commits will be mirrored to this GitHub repo for a while.
• Google's internal use of Mangle effectively forked and will be maintained independently. This makes it possible to make backwards-incompatible changes on the road to 1.0.
• Going forward, no Google CLA is necessary for contributing to Mangle.

• Burak