[WIP] Fix drift in recorded workout intervals

[Copilot]

• Review updated copilot instructions and repository context
• Inspect workout timing/drift code and identify remaining gaps
• Run baseline checks (flutter analyze/test) after environment setup
• Implement/adjust timing fix as needed
• Add/adjust focused tests for timing accuracy
• Run targeted tests to validate fixes
• Summarize results and finalize

Original prompt

The time recorded and uploaded to Strava during workouts is slowly drifting on each interval, causing the recorded workout to be shorter than the actual workout was. I've attached a picture to help visualize this. The red line is the actual workout power graph, the blue line is the recorded power by this app. You can see how the blue peaks slowly drift backwards in relation to the red peaks over time. Please analyze this and make changes to this branch PR that will fix this. The Actual workout was 1:03 and we only recorded 59 minutes.

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