Make FiniteHeightLattice extend Lattice and derive Top/Bot

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lean/Spa/Lattice/Unit.lean

@@ -9,14 +9,8 @@ lemma boundedChains_of_subsingleton (α : Type*) [Preorder α] [Subsingleton α]
   exact (c.step ⟨0, by omega⟩).ne (Subsingleton.elim _ _)
 
 instance : FiniteHeightLattice PUnit where
-  bot := PUnit.unit
-  top := PUnit.unit
-  height := 0
-  longestChain :=
-    { series := RelSeries.singleton _ PUnit.unit
-      head_series := rfl
-      last_series := rfl
-      length_series := rfl }
+  toLattice := inferInstance
+  longestChain := RelSeries.singleton _ PUnit.unit
   chains_bounded := boundedChains_of_subsingleton PUnit 0
 
 end Spa