Unable to obtain and re-apply defaults used during initialisation

I'd love to be able to conveniently retrieve the defaults provided during initialization so i can "reset to defaults" in my app.
However, it would appear these defaults aren't saved anywhere within the PrefServiceShared. At first glance i thought no problem, i can just extend PrefServiceShared, cache my defaults add a getter then i realized PrefServiceShared is closed for extension. :(

for context:

  final service = await PrefServiceShared.init(
    defaults: {
      'pref_a': 0,
      'pref_b': 0,
      'pref_c': 5000,
      'pref_d': 500,
      'pref_e': 4500,
    },
  );

...
// meanwhile.. in some code far far away..
...
PrefService.of(context).resetToDefaults();  // <<--- new function

// AND/OR

PrefService.of(context).resetToDefault('pref_d');  // <<---- another new function.
...

Start by reading PrefServiceShared.init and the PrefService.of(context) entry point to understand how initialization defaults are handled. Define how defaults are retained and exposed for both resetting all preferences and resetting one key, then verify that both requested reset calls restore the values shown in the issue.