RUM-7107 feat: Add Interaction To Next View metric in RUM

[ncreated]

What and why?

📦⏱️ This PR introduces the Interaction-to-Next-View (ITNV) metric to measure the time between the last action in a previous view and the moment the next view is started. This metric provides valuable insights into the time it takes for a view to be prepared and displayed after user interaction.

The ITNV value is reported under the following conditions:

• The value is tracked only if a .tap, .click, or .swipe action occurred in the previous view, and the time between the last action and the start of the next view is less than 3 seconds
• For .tap and .click, the measurement starts at the action's start time.
• For .swipe, the measurement starts at the action's end time.

Example: In the scenario below, A2 is the last action in the "Previous View." It’s a .tap action that occurs less than 3 seconds before the "Next View" starts. The ITNV value for "Next View" is calculated as the time from when the action starts to when the next view starts:

The ITNV value is reported in the view.interaction_to_next_view_time attribute, in nanoseconds.

This is the counterpart to Android PR #2417.

How?

The metric is modeled as an object implementing the ITNVMetricTracking interface, which tracks key events (action, view start, and view completion) and provides a method to retrieve the ITNV value:

internal protocol ITNVMetricTracking {
    func trackAction(startTime: Date, endTime: Date, actionType: RUMActionType, in viewID: RUMUUID)
    func trackViewStart(at viewStart: Date, viewID: RUMUUID)
    func trackViewComplete(viewID: RUMUUID)
    func value(for viewID: RUMUUID) -> TimeInterval?
}

The ITNV metric object is created and managed by RUMSessionScope, enabling it to track actions and views throughout the session. When a view or action starts, a reference to this object is passed to the respective RUM scopes, allowing key events to be tracked via the interface.

This design aligns with the solution implemented for the TTNS metric in #2125

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference
• Add CHANGELOG entry for user facing changes
• Add Objective-C interface for public APIs (see our guidelines [internal]) and run make api-surface)

[datadog-datadog-prod-us1]

Datadog Report

Branch report: feature/RUM-7107/vl-itnv-basics
Commit report: d26e770
Test service: dd-sdk-ios

✅ 0 Failed, 461 Passed, 3218 Skipped, 34.35s Total duration (1m 55.22s time saved)

[simaoseica-dd]

Great job!