feat: ios native app hang capture

[bitsandfoxes]

Resolves https://github.com/getsentry/team-gdx/issues/151

What does it do

This PR forwards a new flag EnableAppHangTracking (default true) and a companion AppHangTimeout (default 5s) to sentry-cocoa (mapped to enableAppHangTracking and appHangTimeoutInterval). When enabled on iOS, this automatically replaces the Unity SDK's C# ANR integration at runtime. The Editor's Advanced tab gains separate C# Watchdog and AppHangTracking sections so the two mechanisms are configurable side by side.

Why does it do it

On iOS, the Unity player loop runs on the main thread (the one with the CFRunLoop). The generated UnityAppController.mm registers Unity's frame tick as a CADisplayLink callback on the main run loop. Every Update, FixedUpdate, and LateUpdate execute on that single thread. Native UIKit events share the same queue.

So when a Unity script blocks (e.g. infinite loop in Update, synchronous I/O, deadlock on .Wait()), it blocks the iOS main run loop directly. sentry-cocoa's watchdog enqueues a block on the main queue and times its execution. If Unity is stuck, that block never runs, and the hang is reported. The generated native event contains an actual stack trace, making the report actionable.

Note: This is not true on macOS. sentry-cocoa does not provide app hang detection there. So EnableAppHangTracking is wired through on iOS only for now. On every other platform the option is currently a no-op.

Result

The resulting native event contains a fully symbolicated stack trace of the C# code that caused the freeze.

Follow up

• We'll need to work on the in-app frames to clean up the stack trace presentation.
• To get AppHangs on macOS: feat: introduce sentry-native on macOS as experimental backend #2687
• To get AppHangs on Windows: feat: native crash backend as option for Windows #2692
• To get AppHangs (ANR) on Android: poc: android anr #2681

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