Fuzz honest multi-instance with incremental network sizes

`FuzzHonestMultiInstance_AsyncAgreement` intermittently fails on CI,
most likely due to taking too long to complete a test.

To avoid intermittent failures:
* Decrease the instance count to 3K
* change the honest multi instance tests to cover incremental network
  sizes, up to 5 for sync and up to 4 for async
* add additional static corpus to the async test for better coverage.

Fixes #251

test/multi_instance_test.go

@@ -75,23 +75,37 @@ func FuzzHonestMultiInstance_AsyncDisagreement(f *testing.F) {
 
 func FuzzHonestMultiInstance_SyncAgreement(f *testing.F) {
 	const (
-		instanceCount = 4000
-		honestCount   = 5
+		instanceCount  = 4000
+		maxHonestCount = 5
 	)
 	f.Add(-47)
 	f.Fuzz(func(t *testing.T, seed int) {
-		multiAgreementTest(t, seed, honestCount, instanceCount, maxRounds, syncOptions()...)
+		t.Parallel()
+		for hc := 2; hc <= maxHonestCount; hc++ {
+			hc := hc
+			t.Run(fmt.Sprintf("%d", hc), func(t *testing.T) {
+				multiAgreementTest(t, seed, hc, instanceCount, maxRounds, syncOptions()...)
+			})
+		}
 	})
 }
 
 func FuzzHonestMultiInstance_AsyncAgreement(f *testing.F) {
 	const (
-		instanceCount = 4000
-		honestCount   = 5
+		instanceCount  = 3000
+		maxHonestCount = 4
 	)
 	f.Add(-7)
+	f.Add(31)
+	f.Add(33)
 	f.Fuzz(func(t *testing.T, seed int) {
-		multiAgreementTest(t, seed, honestCount, instanceCount, maxRounds*2, asyncOptions(seed)...)
+		t.Parallel()
+		for hc := 2; hc <= maxHonestCount; hc++ {
+			hc := hc
+			t.Run(fmt.Sprintf("%d", hc), func(t *testing.T) {
+				multiAgreementTest(t, seed, hc, instanceCount, maxRounds*4, asyncOptions(seed)...)
+			})
+		}
 	})
 }