eth/fetcher, trie: unit test reliability fixes (#23020)

Some tests take quite some time during exit, which I think causes
some appveyor fails like this:

    https://ci.appveyor.com/project/ethereum/go-ethereum/builds/39511210/job/xhom84eg2e4uulq3

One of the things that seem to take time during exit is waiting
(up to 100ms) for the syncbloom to close. This PR changes it to use
a channel, instead of looping with a 100ms wait.

This also includes some unrelated changes improving the reliability of
eth/fetcher tests, which fail a lot because they are time-dependent.

eth/fetcher/block_fetcher_test.go

@@ -698,6 +698,7 @@ func testInvalidNumberAnnouncement(t *testing.T, light bool) {
 	badBodyFetcher := tester.makeBodyFetcher("bad", blocks, 0)
 
 	imported := make(chan interface{})
+	announced := make(chan interface{})
 	tester.fetcher.importedHook = func(header *types.Header, block *types.Block) {
 		if light {
 			if header == nil {
@@ -712,9 +713,23 @@ func testInvalidNumberAnnouncement(t *testing.T, light bool) {
 		}
 	}
 	// Announce a block with a bad number, check for immediate drop
+	tester.fetcher.announceChangeHook = func(hash common.Hash, b bool) {
+		announced <- nil
+	}
 	tester.fetcher.Notify("bad", hashes[0], 2, time.Now().Add(-arriveTimeout), badHeaderFetcher, badBodyFetcher)
+	verifyAnnounce := func() {
+		for i := 0; i < 2; i++ {
+			select {
+			case <-announced:
+				continue
+			case <-time.After(1 * time.Second):
+				t.Fatal("announce timeout")
+				return
+			}
+		}
+	}
+	verifyAnnounce()
 	verifyImportEvent(t, imported, false)
-
 	tester.lock.RLock()
 	dropped := tester.drops["bad"]
 	tester.lock.RUnlock()
@@ -722,11 +737,11 @@ func testInvalidNumberAnnouncement(t *testing.T, light bool) {
 	if !dropped {
 		t.Fatalf("peer with invalid numbered announcement not dropped")
 	}
-
 	goodHeaderFetcher := tester.makeHeaderFetcher("good", blocks, -gatherSlack)
 	goodBodyFetcher := tester.makeBodyFetcher("good", blocks, 0)
 	// Make sure a good announcement passes without a drop
 	tester.fetcher.Notify("good", hashes[0], 1, time.Now().Add(-arriveTimeout), goodHeaderFetcher, goodBodyFetcher)
+	verifyAnnounce()
 	verifyImportEvent(t, imported, true)
 
 	tester.lock.RLock()