tests/fuzzers: improve the fuzzers (#21829)

* tests/fuzzers, common/bitutil: make fuzzers use correct returnvalues + remove output

* tests/fuzzers/stacktrie: fix duplicate-key insertion in stacktrie (false positive)

* tests/fuzzers/stacktrie: fix compilation error

* tests/fuzzers: linter nits

tests/fuzzers/txfetcher/txfetcher_fuzzer.go

@@ -51,8 +51,9 @@ func init() {
 func Fuzz(input []byte) int {
 	// Don't generate insanely large test cases, not much value in them
 	if len(input) > 16*1024 {
-		return -1
+		return 0
 	}
+	verbose := false
 	r := bytes.NewReader(input)
 
 	// Reduce the problem space for certain fuzz runs. Small tx space is better
@@ -124,7 +125,9 @@ func Fuzz(input []byte) int {
 				announceIdxs[i] = (int(annBuf[0])*256 + int(annBuf[1])) % len(txs)
 				announces[i] = txs[announceIdxs[i]].Hash()
 			}
-			fmt.Println("Notify", peer, announceIdxs)
+			if verbose {
+				fmt.Println("Notify", peer, announceIdxs)
+			}
 			if err := f.Notify(peer, announces); err != nil {
 				panic(err)
 			}
@@ -163,8 +166,9 @@ func Fuzz(input []byte) int {
 				return 0
 			}
 			direct := (directFlag % 2) == 0
-
-			fmt.Println("Enqueue", peer, deliverIdxs, direct)
+			if verbose {
+				fmt.Println("Enqueue", peer, deliverIdxs, direct)
+			}
 			if err := f.Enqueue(peer, deliveries, direct); err != nil {
 				panic(err)
 			}
@@ -177,8 +181,9 @@ func Fuzz(input []byte) int {
 				return 0
 			}
 			peer := peers[int(peerIdx)%len(peers)]
-
-			fmt.Println("Drop", peer)
+			if verbose {
+				fmt.Println("Drop", peer)
+			}
 			if err := f.Drop(peer); err != nil {
 				panic(err)
 			}
@@ -191,8 +196,9 @@ func Fuzz(input []byte) int {
 				return 0
 			}
 			tick := time.Duration(tickCnt) * 100 * time.Millisecond
-
-			fmt.Println("Sleep", tick)
+			if verbose {
+				fmt.Println("Sleep", tick)
+			}
 			clock.Run(tick)
 		}
 	}