Improve handling of -short flag in tests (#9075)

As a small developer quality of life improvement, I found many individual unit tests that take longer than around a second to complete, and set them to skip when run under `go test -short`.

On my machine, the wall timings for tests (with `go test -count=1 ./...` and optionally `-short` and `-race`) are roughly:

- Long tests, no race detector: about 1m42s
- Short tests, no race detector: about 17s
- Long tests, race detector enabled: about 2m1s
- Short tests, race detector enabled: about 28s

This PR is split into many commits each touching a single package, with commit messages detailing the approximate timing change per package.

rpc/jsonrpc/client/ws_client_test.go

@@ -65,6 +65,10 @@ func (h *myTestHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 }
 
 func TestWSClientReconnectsAfterReadFailure(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	t.Cleanup(leaktest.Check(t))
 
 	// start server
@@ -97,6 +101,10 @@ func TestWSClientReconnectsAfterReadFailure(t *testing.T) {
 }
 
 func TestWSClientReconnectsAfterWriteFailure(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	t.Cleanup(leaktest.Check(t))
 
 	// start server
@@ -127,6 +135,10 @@ func TestWSClientReconnectsAfterWriteFailure(t *testing.T) {
 }
 
 func TestWSClientReconnectFailure(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	t.Cleanup(leaktest.Check(t))
 
 	// start server

rpc/jsonrpc/jsonrpc_test.go

@@ -340,6 +340,10 @@ func TestRPC(t *testing.T) {
 		}
 	})
 	t.Run("WSClientPingPong", func(t *testing.T) {
+		if testing.Short() {
+			t.Skip("skipping test in short mode")
+		}
+
 		// TestWSClientPingPong checks that a client & server exchange pings
 		// & pongs so connection stays alive.
 		t.Cleanup(leaktest.CheckTimeout(t, 4*time.Second))