👍 Improve performance of isOptionalOf<T>

Before this commit, the benchmark result was

  is.OptionalOf                 243.37 ns/iter   4,108,906.6  (234.5 ns … 271.25 ns) 245.73 ns 264.14 ns 267.17 ns
  is.OptionalOf (pre)           200.66 ns/iter   4,983,517.6 (195.82 ns … 232.95 ns) 202.55 ns 215.28 ns 222.94 ns

And after this commit

  is.OptionalOf                  45.56 ns/iter  21,948,235.7   (41.91 ns … 72.25 ns)  48.58 ns  53.75 ns  56.55 ns
  is.OptionalOf (pre)            12.86 ns/iter  77,733,516.2    (12.7 ns … 20.59 ns)  12.86 ns  14.23 ns  14.64 ns

Author: lambdalisue

is.ts

@@ -390,9 +390,12 @@ export type OptionalPredicate<T> = Predicate<T | undefined> & {
 export function isOptionalOf<T>(
   pred: Predicate<T>,
 ): OptionalPredicate<T> {
-  return Object.assign(isOneOf([isUndefined, pred]), {
-    optional: true as const,
-  });
+  return Object.assign(
+    (x: unknown): x is Predicate<T | undefined> => isUndefined(x) || pred(x),
+    {
+      optional: true as const,
+    },
+  ) as OptionalPredicate<T>;
 }
 
 export default {