Validated has been deprecated, and is no longer included in Arrow.

This patch backports ValidatedNel as an alias of an underlying type, and
maintains the existing extensions.

Continuations have been deprecated in favour of the Raise DSL.

I have removed OutcomeEagerEffect scope, as the Raise DSL does not
expose an eager implementation to be extend. Instead, the expectation is
that the caller wraps calls in `eagerEffect`. This binds the suspended
function to an eager context.

kotest-extensions-arrow has not yet been upgrade to arrow 2.0.0, so
we're seeing compatibility issues with some of the older
implementations.

In the meantime, we can add our own Arb to make tests pass.