Fuzz fixes (#73)

* remove old fuzz corpus and stick to using PCG for seeding fuzz test

* polish up drain logic and reduce action search space

* improve fuzzing debug prints

* more fuzz fixes also formatter capture printer fixes

* refactor StackSeeded test

* fix challenge ack infinite packet bug

* more expressive challenge satisfy

* remove printing

tcp/handler_test.go

@@ -934,7 +934,7 @@ func TestChallengeACKWithBufferedData(t *testing.T) {
 	if err == nil {
 		t.Fatal("expected error from out-of-order segment")
 	}
-	if !server.scb.challengeAck {
+	if !server.scb.pendingChallengeAck() {
 		t.Fatal("challengeAck flag not set after out-of-order segment")
 	}
 	if server.State() != StateEstablished {