f comment why its an f64

Author: TheBlueMatt

lightning/src/routing/scoring.rs

@@ -1817,6 +1817,11 @@ mod bucketed_history {
 		// Because the first thing we do is check if `total_valid_points` is sufficient to consider
 		// the data here at all, and can return early if it is not, we want this to go first to
 		// avoid hitting a second cache line load entirely in that case.
+		//
+		// Note that we store it as an `f64` rather than a `u64` (potentially losing some
+		// precision) because we ultimately need the value as an `f64` when dividing bucket weights
+		// by it. Storing it as an `f64` avoids doing the additional int -> float conversion in the
+		// hot score-calculation path.
 		total_valid_points_tracked: f64,
 		min_liquidity_offset_history: HistoricalBucketRangeTracker,
 		max_liquidity_offset_history: HistoricalBucketRangeTracker,