feat: Add integration for App Hangs V3

[philprime]

Proof-of-concept for an App Hang integration based on Run Loops

Closes #8118

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🚫	Please consider adding a changelog entry for the next release.

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Please add an entry to CHANGELOG.md to the "Unreleased" section. Make sure the entry includes this PR's number.

Example:

## Unreleased

### Features

- Add integration for App Hangs V3 ([#8117](https://github.com/getsentry/sentry-cocoa/pull/8117))

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[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

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[cursor]

V3 ignores sample hang gates

Medium Severity

experimental.appHangs.enableV3 is hard-coded to true, so App Hang V3 stays on when legacy app hang tracking is turned off for benchmarking or via --io.sentry.app-hangs.disable-tracking, unlike enableAppHangTracking on the line above.

 

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[cursor]

Sample enables dual hang trackers

Medium Severity

Turning on App Hang V3 here leaves enableAppHangTracking enabled in the normal sample path, so both SentryHangTrackerIntegrationObjC and SentryHangTrackingV3Integration install and can each emit fatal hang events for the same stall.

 

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[sentry]

Bug: The hitchDurationCounter incorrectly accumulates a cumulative duration value on each callback, leading to a wildly inflated total hang duration.
_{Severity: HIGH}

Suggested Fix

The hitchDurationCounter should not be incremented when isOngoing is true. The duration should only be recorded from the final callback when isOngoing is false, as that duration value already represents the total hang time. Alternatively, calculate and add an incremental delta within processHitch instead of the cumulative duration.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: Sources/Swift/Integrations/HangTracking/AppHangDetection.swift#L56

Potential issue: The `processHitch` function is called repeatedly during an ongoing
hang. On each call, it adds the `duration` argument to `hitchDurationCounter`. However,
the `duration` passed is the total elapsed time since the hang started, not an
incremental delta. This causes the counter to accumulate an arithmetic series of
cumulative values, resulting in a significantly overestimated hang duration. For
example, a 2-second hang could be miscalculated as an 81-second hang. This leads to
hangs being reported incorrectly when they are below the threshold and sending
inaccurate duration data.

_{Did we get this right? 👍 / 👎 to inform future reviews.}