rake setup_ai_gateway reports incorrect duration

Problem Statement

This is a regression introduced by #3063 (closed).

While looking into the data in #3063 (comment 2931665378), I noticed the GDK dashboard shows rake setup_ai_gateway taking an average of 9 seconds and p90 of 15 seconds, but the component times add up to 1.67-2 minutes.

Impact

We can't accurately measure setup performance.

Proposal

Fix the duration measurement logic to capture the actual execution time.

Impacted categories

The following categories relate to this issue:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.