ThinEvent reason and livemode

[jar-stripe]

Why?

V2 ThinEvent payloads contain a livemode boolean and optionally a reason object that contains metadata about the event and object that triggered it. This PR ensures these fields are exposed in ThinEvent, and adds tests to verify they are parsed correctly.

What?

• added EventReason and EventReasonRequest types to thin_event.rb
• added attr_reader entries for livemode and reason to ThinEvent
• added test for parsing v2 thin events with livemode and reason, and test for reason == nil in existing parse v2 event test

Changelog

• Add livemode and optional reason fields to ThinEvent