Add Android push notification delivery

[andremion]

Goal

The Android e2e suite needs to deliver push notifications, which no client network path carries (they arrive through the OS). The iOS side of /participant/push uses xcrun simctl push, which only works on iOS simulators. This adds an Android delivery branch to the same endpoint.

Implementation

When /participant/push receives a component param (the app's broadcast receiver), it builds the Stream FCM data payload (version, sender, type, message_id, cid, channel_id, channel_type, title, body) and delivers it with adb shell am broadcast. The receiver in the app under test feeds it into the client SDK's real validation and notification path.

The rest degradations mirror the iOS semantics against the Android payload contract: null and empty degrade the optional title and body while keeping the routing keys valid (so the push still appears), incorrect_type and incorrect_data add junk badge fields, and invalid_version/invalid_sender/invalid_type break a required key so the client validator drops the push. The iOS branch is unchanged.

Testing

Driven by the ported Android push notification e2e tests (PushNotificationTests in GetStream/stream-chat-android), all 7 verified locally against this branch on a Pixel 8 API 35 emulator.

[andremion]

Started e2e tests on this branch:

• Android
• iOS

[andremion]

Re-ran e2e after updating this branch with main, which now includes the truncation flake fix (#48):

• Android
• iOS