feat(num): add formatNumber function with caching of the formatter

Author: adaptive-shield-matrix

src/num/formatNumber.ts

@@ -0,0 +1,11 @@
+let numberFormat: Intl.NumberFormat | undefined = undefined
+let numberFormatLocale: string | undefined = undefined
+
+export function formatNumber(num: number, locale?: string) {
+  if (locale === numberFormatLocale && numberFormat) {
+    return numberFormat.format(num)
+  }
+  numberFormat = new Intl.NumberFormat(locale)
+  numberFormatLocale = locale
+  return numberFormat.format(num)
+}