eth: replace topN helper with stdlib slices.SortedFunc + DeleteFunc

Remove the custom topN generic function. Use slices.SortedFunc
(creates a sorted copy from an iterator) + slices.DeleteFunc (filters
score <= 0) from the standard library. No custom generics needed.

eth/dropper.go

@@ -17,9 +17,9 @@
 package eth
 
 import (
+	"cmp"
 	mrand "math/rand"
 	"slices"
-	"sort"
 	"sync"
 	"time"
 
@@ -189,25 +189,6 @@ func (cm *dropper) dropRandomPeer() bool {
 	return true
 }
 
-// topN returns the top n elements from items by score (descending).
-// Only elements with score > 0 are included. The input slice is not modified.
-func topN[T any](items []T, n int, score func(T) float64) []T {
-	if n == 0 || len(items) == 0 {
-		return nil
-	}
-	cp := make([]T, len(items))
-	copy(cp, items)
-	sort.Slice(cp, func(i, j int) bool { return score(cp[i]) > score(cp[j]) })
-
-	var result []T
-	for i := 0; i < n && i < len(cp); i++ {
-		if score(cp[i]) > 0 {
-			result = append(result, cp[i])
-		}
-	}
-	return result
-}
-
 // protectedPeers computes the set of peers that should not be dropped based
 // on inclusion stats. Each protection category independently selects its
 // top-N peers per inbound/dialed pool; the union is returned.
@@ -228,18 +209,29 @@ func (cm *dropper) protectedPeers(peers []*p2p.Peer) map[*p2p.Peer]bool {
 			dialed = append(dialed, p)
 		}
 	}
+	// protectPool selects the top-frac peers from pool by score and adds them to result.
 	result := make(map[*p2p.Peer]bool)
+	protectPool := func(pool []*p2p.Peer, score func(*p2p.Peer) float64, frac float64) {
+		n := int(float64(len(pool)) * frac)
+		if n == 0 {
+			return
+		}
+		sorted := slices.SortedFunc(slices.Values(pool), func(a, b *p2p.Peer) int {
+			return cmp.Compare(score(b), score(a)) // descending
+		})
+		top := slices.DeleteFunc(sorted[:min(n, len(sorted))], func(p *p2p.Peer) bool {
+			return score(p) <= 0
+		})
+		for _, p := range top {
+			result[p] = true
+		}
+	}
 	for _, cat := range protectionCategories {
-		// Build a score function that looks up the peer's stats.
 		score := func(p *p2p.Peer) float64 {
 			return cat.score(stats[p.ID().String()])
 		}
-		for _, p := range topN(inbound, int(float64(len(inbound))*cat.frac), score) {
-			result[p] = true
-		}
-		for _, p := range topN(dialed, int(float64(len(dialed))*cat.frac), score) {
-			result[p] = true
-		}
+		protectPool(inbound, score, cat.frac)
+		protectPool(dialed, score, cat.frac)
 	}
 	if len(result) > 0 {
 		log.Debug("Protecting high-value peers from drop", "protected", len(result))