refactor(http)!: fix cascade dart good practices + docs

packages/wyatt_http_client/lib/src/utils/delay.dart

@@ -17,7 +17,9 @@
 import 'dart:core';
 import 'dart:math';
 
+/// Defines some delay functions.
 abstract class Delay {
+  /// Returns a delay based on the [attempt].
   static Duration getRetryDelay(int attempt) {
     assert(attempt >= 0, 'attempt cannot be negative');
     if (attempt <= 0) {