[improvement] rename packages dir to src (#3659)

src/utils/format/unit.ts

@@ -0,0 +1,11 @@
+import { isDef } from '..';
+import { isNumber } from '../validate/number';
+
+export function suffixPx(value?: string | number): string | undefined {
+  if (!isDef(value)) {
+    return undefined;
+  }
+
+  value = String(value);
+  return isNumber(value) ? `${value}px` : value;
+}