[1.x] Rename fields method and return an object

[jessarcher]

This PR makes a minor tweak to the unreleased changes in #251, based on what felt better when writing the docs.

It renames the fields method to find and returns an object instead of an array because objects feel nicer to work with in Blade views.

Before

$users = Pulse::resolveUsers($aggregates->pluck('key'));

$aggregates->map(fn ($aggregate) => (object) [
    'user' => (object) $users->fields($aggregate->key),
    // ...
]);

After

$users = Pulse::resolveUsers($aggregates->pluck('key'));

$aggregates->map(fn ($aggregate) => (object) [
    'user' => $users->find($aggregate->key),
    // ...
]);