Function isExactNumber

src/compute-engine/boxed-expression/apply.ts:59–63

(x: Expression)

 * Eisenstein series at τ = i) are preserved. A non-Gaussian complex float
 * (`1.5+2i`) still numericizes — it never was representable exactly.
 *
 * Non-number-literal expressions (symbols like `Pi`, unevaluated functions)
 * are treated as exact here: they have no float to lose, and any exact
 * reduction for them is the caller's job, not this predicate's.
 */
export function isExactNumber(x: Expression): boolean {
  if (!isNumber(x)) return true;
  if (x.isExact) return true;