Pushy v0.15.3 - live activities and push-to-talk notifications

This is a minor release that:

• Adds support for new Live Activity features (thank you, @louise-scully!)
  • Relaxes the bounds on relevance scores in push notification payloads (scores are no longer bounded between 0.0 and 1.0)
  • Adds support for the stale-date payload field
• Allows callers to opt in to protocol negotiation when opening new connections (thank you, @MarcelHeckel!)
• Adds support for the apns-unique-id response header available in the APNs development environment (thank you, @hectorespert!)
• Improves performance and resolves a potential inconsistency when verifying authentication tokens in the mock server

For a complete list of changes, plese see the v0.15.3 milestone or the commits between 0.15.2 and 0.15.3.