Remove Left/Right/None/Nil implicit schemas

[vigoo]

Currently we have implicit schemas for

• Left and Right
• None
• Nil

and these schemas are not (necessarily) compatible with the schema of Either, Option and List. This leads to serialization errors in places where the schema is captured for polymorphic types such as in zio-flow:

zio/zio-flow#191

In this example if some zio-flow function is called with Nil the implicit Schema.nil was used for serialization but that was later assumed to be a List[A] and deserialization of that raw value fails.

Previously I made left and right schemas compatible with the either schema. An alternative solution to the problem would be to try doing the same with none and nil but I felt like it's more correct to just get rid of these implicits and force the users (of zio-schema) to know exactly what type they need schema for.

This means we can no longer get an implicit schema for Nil without having an implicit schema for a given A that would be the element type - but I think this is a valid assumption.

In polymorphic cases like the linked one, replacing Nil with List.empty[A] for example makes the compiler able to infer the proper types and find the implicit which I think is a good compromise.

I removed left and right too just to make the approach the same for all of these.