## Context

By design, GraphQL can create a lot of N+1. The `graphql` gem provides
[a way to inspect the
query](https://graphql-ruby.org/queries/lookahead.html) and eager load
accordingly.

This is generally not an issue because Lago's vast majority of the load
is on the REST API, not the dashboard. But still, it can lead to slow
page loading.

## Description

In the SubscriptionAlertResolver, a query can trigger 2 extra requests
per item, one for thresholds, one for billable metric.

With lookahead, we check if billableMetric or thresholds are request end
ensure we call `includes(:billable_metric)` or `includes(:thresholds)`
respectively.

Another useful technique is to also [expose ids alongside the
relationships](#3692), like in
the Alert Object.

### How to use

* Add `extras` Resolver configuration
* Make sure you receive the `lookahead:` named argument
* Explore lookahead object with `selection` and `select?`

```ruby
class SomethingResolver < Resolvers::BaseResolver
  REQUIRED_PERMISSION = "something:view"

  # Explicitly tell GraphQL that you want to use `lookahead`
  extras [:lookahead]

  argument :limit, Integer, required: false
  argument :page, Integer, required: false

  type Types::Something::Object.collection_type, null: false

  def resolve(lookahead:, limit: nil, page: nil) # Automatically receive lookahead
    scope = Something.all

    # Notice the :collection outer object
    if lookahead.selection(:collection).selects?(:organization)
      scope = scope.includes(:organization)
    end

    if lookahead.selection(:collection).selection(:organization).selects?(:billing_entity)
      scope = scope.includes(organization: :billing_entity)
    end

    scope
  end
end
```

Links:
* https://graphql-ruby.org/queries/lookahead.html
*
https://gist.github.com/DmitryTsepelev/d0d4f52b1d0a0f6acf3c5894b11a52ca

### Testing

This PR also sets up [`bullet` gem for
tests](https://github.com/flyerhzm/bullet?tab=readme-ov-file#run-in-tests),
until now it was only a dev dependency.

Notice the `with_bullet: true` example metadata.

```ruby
context "when doing something" do
  let(:model) { ... }

  it "does something", with_bullet: true do
    #...

    # Must be start manually for maximum flexibility
    Bullet.start_request

    subject # Service.call, gql query, api requests, function call...

    expect(Bullet.notification?).to eq false # Ensure no N+1 !
  end
end
```

We see unexpected memory consumption. We disable lookahead to see if
it's the origin of the issue.

See #3695 for original work