feat: meaningful comments for internal packages

internal/statistics/tracker.go

@@ -6,11 +6,13 @@ import (
 	"time"
 )
 
+// An observer, to track reduction performance.
 type Tracker struct {
 	start time.Time
 	steps uint64
 }
 
+// Create a new reduction performance tracker.
 func Track() *Tracker {
 	return &Tracker{}
 }