feat(progression): Profile aggregate (slice 4)

best times only improve; achievement unlock announces on the transition
only, so popup/Steam subscribers cannot double-fire; statistics are
increase-only (IncrementStat took any int).

RelockAchievement is console-only and documented as not reaching Steam -
a Steam achievement cannot be un-earned, so the disagreement is
permanent and deliberate.

refactor: extract EventLog, composed by both aggregates now that the
duplication actually exists. 34 tests.

progression/LevelTime.cs

@@ -4,7 +4,7 @@ namespace Mr.BrickAdventures.Progression;
 /// A completion time for one Level. Strictly positive — a zero time means the clock was never
 /// running, which is a defect rather than a fast run.
 /// </summary>
-public readonly struct LevelTime
+public readonly struct LevelTime : IEquatable<LevelTime>
 {
     public double Seconds { get; }
 
@@ -13,4 +13,11 @@ public readonly struct LevelTime
     public static LevelTime Of(double seconds) => double.IsFinite(seconds) && seconds > 0
         ? new LevelTime(seconds)
         : throw new ArgumentOutOfRangeException(nameof(seconds), seconds, "A completion time must be a finite positive number.");
+
+    public bool IsFasterThan(LevelTime other) => Seconds < other.Seconds;
+
+    public bool Equals(LevelTime other) => Seconds.Equals(other.Seconds);
+    public override bool Equals(object? obj) => obj is LevelTime other && Equals(other);
+    public override int GetHashCode() => Seconds.GetHashCode();
+    public override string ToString() => $"{Seconds:0.###}s";
 }