Lean migration: Phase 6 (forward analysis framework)

- Spa.Analysis.Forward.Lattices: VariableValues/StateVariables (FiniteMap
  instantiations), fixed heights, variablesAt, joinForKey/joinAll, interpV
  and its sup/foldr lemmas
- Spa.Analysis.Forward.Evaluation: StmtEvaluator/ExprEvaluator + validity
  (the Agda Valid* instance records become plain Props)
- Spa.Analysis.Forward.Adapters: expr-to-stmt evaluator adapter + validity
- Spa.Analysis.Forward: updateAll, analyze, result (least fixpoint via the
  gas-based Fixedpoint), walkTrace, analyze_correct — the framework's main
  soundness theorem

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lean/Spa/Analysis/Forward/Evaluation.lean

@@ -0,0 +1,44 @@
+/-
+Port of `Analysis/Forward/Evaluation.agda`.
+
+Correspondence:
+  StmtEvaluator (eval, eval-Monoʳ)  ↦ StmtEvaluator (eval, eval_mono)
+  ExprEvaluator (eval, eval-Monoʳ)  ↦ ExprEvaluator (eval, eval_mono)
+  IsValidExprEvaluator              ↦ IsValidExprEvaluator
+  IsValidStmtEvaluator              ↦ IsValidStmtEvaluator
+  ValidExprEvaluator,
+  ValidStmtEvaluator (records)      ↦ (the `IsValid…` Props are passed
+                                      directly; the wrapper records existed
+                                      for Agda instance resolution)
+-/
+import Spa.Analysis.Forward.Lattices
+
+namespace Spa
+
+variable (L : Type) [Lattice L] (prog : Program)
+
+/-- Agda: `StmtEvaluator`. -/
+structure StmtEvaluator where
+  eval : prog.State → BasicStmt → VariableValues L prog → VariableValues L prog
+  eval_mono : ∀ s bs, Monotone (eval s bs)
+
+/-- Agda: `ExprEvaluator`. -/
+structure ExprEvaluator where
+  eval : Expr → VariableValues L prog → L
+  eval_mono : ∀ e, Monotone (eval e)
+
+variable {L prog}
+
+/-- Agda: `IsValidExprEvaluator`. -/
+def IsValidExprEvaluator (E : ExprEvaluator L prog)
+    (I : LatticeInterpretation L) : Prop :=
+  ∀ {vs : VariableValues L prog} {ρ : Env} {e : Expr} {v : Value},
+    EvalExpr ρ e v → interpV I vs ρ → I.interp (E.eval e vs) v
+
+/-- Agda: `IsValidStmtEvaluator`. -/
+def IsValidStmtEvaluator (E : StmtEvaluator L prog)
+    (I : LatticeInterpretation L) : Prop :=
+  ∀ {s : prog.State} {vs : VariableValues L prog} {ρ₁ ρ₂ : Env} {bs : BasicStmt},
+    EvalBasicStmt ρ₁ bs ρ₂ → interpV I vs ρ₁ → interpV I (E.eval s bs vs) ρ₂
+
+end Spa