Unify ConditionalFormula evaluation and add algebraic fusion for chained NaturalArray transforms

[Copilot]

Implements the ConditionalFormula O(1) step by compiling conditional branches into a single arithmetic expression where purity allows, while preserving fallback semantics for non-encodable cases. It also closes key optimization gaps in simplification and introduces lazy fusion behavior for chained map/filter/zip over NaturalArray views.

• ConditionalFormula expression unification

  • Converts branch chains into one indicator-weighted expression (c*A + (1-c)*B folded from tail to head).
  • Keeps runtime on the expression path to a single evaluate(...) per index for encodable formulas.
  • Preserves branch-statement fallback when purity/pattern checks fail.

• Numeric condition layer + constant folding

  • Adds boolean→numeric indicator lowering (and/or/!, comparison forms) with pure-only gating.
  • Adds compile-time boolean folding for constant conditions (including literal comparisons), eliminating dead branches early.

• Simplification pass expansion

  • Adds structural and algebraic reductions:
    • a-a -> 0
    • a+a -> 2*a
    • (a*b)+(a*c) -> a*(b+c) (common-factor extraction)
    • c*A + (1-c)*A -> A
  • Adds numeric literal folding for +, -, *, and exact integer /.

• Formula lifecycle in NaturalArray

  • Keeps one active conditional formula by composing new formulas with existing formula state, preserving precedence while avoiding growth of independent conditional entries.

• Lazy map/filter/zip fusion in LiteralRegistry

  • Composes chained lazy map views (map(...).map(...)) into a single mapper pipeline.
  • Composes chained lazy filter views (filter(...).filter(...)) into a single predicate pipeline.
  • Extends zip source handling to consume lazy map/filter views directly.

• Coverage updates

  • Extends ConditionalFormulaOptimization.cod with:
    • constant-true / constant-false condition cases
    • chained map/filter fusion cases
    • zip over mapped arrays case

// Unified conditional expression fold (tail -> head)
Expr unified = elseExpr;
for (int i = indicators.size() - 1; i >= 0; i--) {
    Expr c = indicators.get(i);
    Expr a = branches.get(i);
    unified = (c * a) + ((1 - c) * unified);
}