Function factorial

test/big-decimal/precision-comparison.test.ts:47–51

* Compute factorial as a BigDecimal string.

(n: number)

 * Compute factorial as a BigDecimal string.
 */
function factorial(n: number): string {
  let result = 1n;
  for (let i = 2; i <= n; i++) result *= BigInt(i);
  return result.toString();
}

function withPrecision<T>(prec: number, fn: () => T): T {
  const savedBD = BigDecimal.precision;