Upgrade to ZIO 2.0

[swoogles]

ZIO 2.0 is at Milestone 4, with an RC expected in the next few weeks.
https://github.com/zio/zio/releases/tag/v2.0.0-M4

The API is nearly stable at this point, so any early migration work against this version should pay off towards the official 2.0 release.

The progress is being tracked here:
zio/zio#5470

The Stream Encoding work in progress is the only area where the API might still change before the RC.

We are actively working on a ScalaFix rule that will cover the bulk of the simple API changes:
https://github.com/zio/zio/blob/series/2.x/scalafix/rules/src/main/scala/fix/Zio2Upgrade.scala
We highly recommend starting with that, and then working through any remaining compilation errors :)

To assist with the rest of the migration, we have created this guide:
https://zio.dev/howto/migrate/zio-2.x-migration-guide/

If you would like assistance with the migration from myself or other ZIO contributors, please let us know!