Recalculate pit durations using car and track specific timings
When a saved strategy has a specific car and track combination set, update pit stop durations to use accurate timings for that car's race class and track/layout, instead of using estimated averages. This ensures time loss calculations for fuel-saving strategies are based on the actual pit durations.
The flatout strategy is processed first before other strategies to ensure time loss calculations use the updated flatout as baseline.
Also refactors tire change logic into StintService.ShouldChangeTyres to eliminate duplication between RaceStrategy and Stint services.
Co-Authored-By: Claude noreply@anthropic.com
Resolves #86 (closed) #115 (closed)