⚠️ Add strongly typed EventNotifications

[xavdid-stripe]

Why?

As part of the Next-Gen Event Handling project, we're adding fully typed classes to represent all the thin events Event Notifications a user could receive. There are also helper methods that help with the event handling experience.

What?

• (see changelog below for user-facing changes)
• add tests
• fix doc typos
• TKTK

See Also

DEVSDK-2662

Changelog

We've overhauled how V2 Events are handled in the SDK! This approach should provide a lot more information at authoring and compile time, leading to more robust integrations. As part of this process, there are a number of changes to be aware of.

• ⚠️ Renamed Stripe::ThinEvent to Stripe::EventNotification
• ⚠️ Renamed StripeClient.parse_thin_event to StripeClient.parse_event_notification and changed its method signature accordingly
• Added matching EventNotification classes to every v2 Event. For example, there's now a V1BillingMeterErrorReportTriggeredEventNotification to match the existing V1BillingMeterErrorReportTriggeredEvent. Each notification class defines a fetch_event() method to retrieve its corresponding event. For events with related objects, there's a fetch_related_object() method that performs the API call and casts the response to the correct type.
• Added UnknownEventNotification to help with handling unknown event types