Optimize liftOutcome in KleisliGenSpawn to avoid allocation

[nmichael44]

Calling bothOutcome or racePair on a Kleisli evaluates liftOutcome,
which currently instantiates a new FunctionK and routes it through mapK.

This commit replaces the mapK invocation with a direct pattern match
on the Outcome. This optimization:

1. Eliminates the FunctionK allocation on every invocation.
2. Bypasses the evaluation overhead of mapK.
3. Aligns the Kleisli implementation with OptionT, EitherT, IorT,
   and WriterT in GenSpawn.scala, which already use this exact
   pattern-matching technique.