Support for Scala 3

[saeltz]

Teleproto is a huge macro for Scala 2. Metaprogramming has been reworked from the ground up for Scala 3 and is totally different. New macros will have to be written.

We decided to start working on the new branch https://github.com/moia-oss/teleproto/tree/scala3 and will open PRs tackling the implementation until we have a working version 3.0 of Teleproto for Scala 3. Compilation and tests are expected to fail for some time. Once we have the working version, the scala3 branch will become the master.

For now, we decided to not support the Migration macro and focus on Reader & Writer. That may come later in a version 3.1.

This ticket tracks the progress:

• Support the Reader & Writer macros
• Support the Migration macro
• ...