Shai: Update to ZIO2

[shonfeder]

Our zio-grpc now has support for ZIO2 (tho it is currently via a -testn suffixed release). This opens the way for us to update, which we should do sooner than later, as the longer we wait the higher the maintenance cost of migrating.

This will require updates to all our zio libs, along with migration of the existing use of ZIO code to adapt to the breaking changes in the library.

[shonfeder]

While it would be nice in theory to make this migration prior to doing any more substantial work on Shai, not all of our dependencies currently have stabilized support for ZIO2 (notably especially zip-grpc).

So we'll proceed with features in the meantime. Fortunately, it looks like a good part of the migration can be automated. See https://zio.dev/guides/migrate/zio-2.x-migration-guide/