fix: Change trackDuration argument from float to double

[mattrmc1]

Note

Medium Risk
Public interface signature change on ILdAiConfigTracker is a binary-breaking change for external implementers, though call sites passing float literals still compile via implicit widening.

Overview
ILdAiConfigTracker.TrackDuration and LdAiConfigTracker.TrackDuration now take double durationMs instead of float, matching how durations are already stored internally and how Stopwatch.Elapsed.TotalMilliseconds / AiMetrics.DurationMs are produced.

Internal call sites in TrackDurationOf and TrackMetricsOf no longer cast millisecond values to float before recording. Unit tests were updated to pass double literals where they exercise TrackDuration directly.

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