Morph

Picks the direction to morph a pair of optics into a shared carrier so .andThen works across carriers. Four givens, decreasing priority:

• Morph.same — same carrier, no morph (Out = F).
• Morph.leftToRight — morph left into G via Composer[F, G] (Out = G).
• Morph.rightToLeft — morph right into F via Composer[G, F] (Out = F).
• LowPriorityMorphInstances.bothViaAffine — both into Affine when neither bridges directly (covers e.g. Prism ∘ Lens).

cats-eo ships essentially one bidirectional Composer pair — forget2multifocus / multifocus2forget (the latter restricted to T = Unit). For every other carrier pair at most one of the first three fires; for that one pair a Forget[F] ⇄ MultiFocus[F] chain can be ambiguous, resolved by routing through the explicit Composer[..].to(o) form (see multifocus2forget's docstring).