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.

light/detector_test.go

@@ -235,6 +235,10 @@ func TestLightClientAttackEvidence_Equivocation(t *testing.T) {
 }
 
 func TestLightClientAttackEvidence_ForwardLunatic(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	// primary performs a lunatic attack but changes the time of the header to
 	// something in the future relative to the blockchain
 	var (

light/example_test.go

@@ -17,6 +17,10 @@ import (
 
 // Manually getting light blocks and verifying them.
 func TestExampleClient(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 	conf, err := rpctest.CreateConfig(t, "ExampleClient_VerifyLightBlockAtHeight")

light/light_test.go

@@ -23,6 +23,10 @@ import (
 
 // Automatically getting new headers and verifying them.
 func TestClientIntegration_Update(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	t.Parallel()
 
 	ctx, cancel := context.WithCancel(context.Background())
@@ -84,6 +88,10 @@ func TestClientIntegration_Update(t *testing.T) {
 
 // Manually getting light blocks and verifying them.
 func TestClientIntegration_VerifyLightBlockAtHeight(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	t.Parallel()
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
@@ -162,6 +170,10 @@ func waitForBlock(ctx context.Context, p provider.Provider, height int64) (*type
 }
 
 func TestClientStatusRPC(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 	conf, err := rpctest.CreateConfig(t, t.Name())

light/provider/http/http_test.go

@@ -33,6 +33,10 @@ func TestNewProvider(t *testing.T) {
 }
 
 func TestProvider(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 	cfg, err := rpctest.CreateConfig(t, t.Name())